As President Bush prepares for his first meeting with a senior Chinese official, his administration faces two military decisions that could put the United States on a collision course with China while the Bush administration is barely under way.

The issues are whether to design a national missile defense capable of countering China's small nuclear force and whether to sell destroyers equipped with the Aegis radar system to Taiwan.

Both matters are of great concern to China, especially the sale of the Aegis. It fears that the $1-billion-a-ship system could eventually become a platform for a regional missile shield for Taiwan and could usher in a new level of American military cooperation with the island, which China considers a renegade province.

And both decisions are also dear to the hearts of conservative Republicans, who are deeply suspicious of China and represent an important constituency for the new president. Mr. Bush played to this sentiment in a major address on national defense in September 1999 by underscoring the need to counter the Chinese missile treat.

China has indicated that it is ready to begin a dialogue on missile defenses when Deputy Prime Minister Qian Qichen meets with Mr. Bush this week in Washington. But the issue remains politically charged, the Chinese are adamantly opposed to the Aegis sale and reaching a long- term accommodation with Beijing may prove elusive.

"The Chinese may be open to the idea of a discussion with us," an American expert said. "But I don't think you will get this administration to come out and say that it is the U.S. national interests for China to have a stable deterrent — that is, that it is in the American interest for China to be able to incinerate an American city."

Though Russian and Chinese objections to an American missile defense are often lumped together, the two nations' circumstances are vastly different. Russia is a power in decline and is viewed mainly as a menace to itself. In Washington, however, China is increasingly seen as a growing regional power that will compete with the United States for dominance of the western Pacific.

The structure of Russian and Chinese missile forces also differ radically. When it comes to long-range nuclear arms, the Russians have more than enough missiles to overwhelm a limited American defense. In contrast, China has only 18 DF-5 long-range intercontinental missiles that are capable of reaching the United States, with aging liquid- fueled systems whose warheads are kept separately.

Russia has also taken the position that if new missile defenses are to be developed, they should be "theater" systems, capable of countering medium- and short-range rockets, not those in Russia's strategic arsenal. It has even offered to join the United States' European allies in building such a system.

But the deployment of theater defenses is a big worry for the Chinese. They would potentially counter the more than 100 medium-range missiles China has within range of India, Japan and American forces in the Pacific. While China's DF-21 medium-range missiles can overwhelm current theater defenses, future theater antimissile systems might be more capable and linked to an American national missile defense system.

Then there is Taiwan, which has made the United States' efforts to develop national and theater missile defenses even more of a worry. To put pressure on Taiwan to accept Beijing's sovereignty, the Chinese have placed about 300 short-range missiles near the island, American specialists say, and are expanding that force at a rate of 50 missiles a year.

China fears that deployment of theater missile defenses for Taiwan could enable the island to resist that pressure, lead to a new level of cooperation with Washington and strengthen pro-independence sentiment on Taiwan. The Chinese also fear that an American missile shield could embolden Washington to intervene militarily in crises around the world, especially in the Taiwan Strait.

"They said that we are seeking absolute security and that if we have a missile defense we will act without any restraint," said a former ranking Clinton administration official who has discussed the missile defense issue with the Chinese. "They used the example of Kosovo. But their real concern was Taiwan."

Even before the Bush administration took office, missile defenses emerged as a major and intractable obstacle to American-Chinese relations.

To counter the potential missile threat from "rogue states" like Iran and North Korea, the Clinton administration developed a two-stage plan. The first phase called for placing 100 interceptors and a battle-management radar system in Alaska. In the second stage, 250 interceptors would have been used, along with additional battle-management radar systems.

The United States sought to soothe Moscow's anxieties by assuring the Kremlin that it would retain the ability to launch a retaliatory strike against the United States. But it was not easy for the Clinton administration to make a similar case to the Chinese.

The Chinese have long planned to upgrade their nuclear force by fielding the DF-31, a solid-fueled mobile missile with the range to strike Alaska and the northwestern United States, as well as a long-range successor. But the Clinton administration's experts concluded that the first phase of the Clinton system might blunt China's current missile force, while the second phase might have some capacity against the updated Chinese deterrent.

American intelligence analysts also concluded that an American shield would goad the Chinese to expand their planned buildup so that China could be sure that it could overwhelm an American defense. That, intelligence analysts said, could set off a chain reaction in South Asia as India responded by building up its arsenal and Pakistan responded to an Indian buildup.

Hoping to head off an arms race in South Asia, the Clinton administration sought to engage the Chinese in a dialogue about missile defense. But the issue proved to be difficult.

The Clinton administration, for instance, considered offering China assurances that it had a right to a nuclear deterrent. But, fearful that this would cause a furor with conservative Republican lawmakers, the administration settled for a vaguer declaration that its missile defense plan was not directed at China.

That formulation side-stepped the issues of whether China was entitled to have a retaliatory capacity against the United States and whether an American defense might be able to shoot down Chinese missiles even though that was not its main purpose.

The technical difficulty of setting up an arms control regime with the Chinese was another factor. Administration experts concluded that it would be very difficult to coordinate the construction of an American defense with the modernization of the Chinese nuclear arsenal so that the Chinese could be assured of retaining a retaliatory nuclear force. The programs would move at different paces.

Because the relationship between the American and Chinese military is not nearly as developed as that between the Americans and the Russians, the Clinton administration was not ready to offer other arrangements, like inviting Chinese officials to visit American factories that make antimissile interceptors or sharing missile-launch data with the Chinese.

In terms of theater missile defenses, the Clinton administration kept its options open. It deferred, but did not reject, Taiwan's request for the Arleigh Burke-class destroyers equipped with the Aegis system.

The arrival of the Bush administration raised the stakes for the Chinese. During his early campaign Mr. Bush got Beijing's attention when he went to the Citadel in Charleston, S.C., in September 1999 to deliver an address on national defense.

The United States not only needed to counter missile threats from "rogue states" like Iraq and North Korea, but also, Mr. Bush warned, should worry about missile threats from China.

"In 1996, after some tension over Taiwan, a Chinese general reminded America that China possesses the means to incinerate Los Angeles with nuclear missiles," Mr. Bush noted ominously.

Since taking office, the Bush administration has yet to outline what sort of antimissile system it plans to build, but it has signaled that it wants to go beyond the sort of limited missile defense proposed by President Clinton.

Secretary of State Colin L. Powell said during his Senate confirmation hearing that such a missile defense would not be directed against China, repeating the Clinton administration's formulation. But some administration officials believe that it would be useful if a future antimissile system had the ability to counter Chinese missiles even thought this might not be its stated purpose.

Laying the groundwork for this week's meetings, China sought to demonstrate some modest flexibility. It signaled that it was prepared at least to discuss the American plans for a missile defense of the United States. And it indicated that it was prepared to accept the development of theater defense to protect American troops in Japan.

Instead, it has focused its energy on trying to block the sale of the Aegis-equipped destroyer system to Taiwan. The purpose of the sale would be to defend Taiwan's Navy, and the destroyers themselves would not be delivered and integrated into Taiwan's fleet for eight years or so. But they represent a potential platform for a theater missile defense should Washington eventually decide to provide one to Taiwan.

So far, the Bush administration's response has been to put the onus on the Chinese. It has cautioned China that the best way to preclude the sale of the Aegis is to reduce the Chinese missile threat to Taiwan. Nor has the administration signaled how it plans to reassure Beijing about the broader goals of its missile defense program.

In a television interview last month, Defense Secretary Donald H. Rumsfeld dismissed China's objections about an American antimissile shield and appeared to leave the door wide open for a theater missile defense for Taiwan.

"China is not a concern," Mr. Rumsfeld said. "It's not a party to the ABM treaty. It is a country that is increasing its defense budgets in double digits year after year."

"I don't believe that anyone can make a case that missile defense is a particular problem to China," he continued. "On the other hand, if some country decided it wanted to be aggressive to its neighbors and acquire additional territory by force, then having a missile defense system is not a bad idea, it seems to me."