China's foremost political prisoner, Wei Jingsheng, arrived in the United States today and was immediately taken to a Detroit hospital for treatment a day after he was freed on medical parole from jail, where he has spent all but six months of the last 18 years.

A spokeswoman for the Henry Ford Hospital confirmed Wei, 47, was in fair but stable condition and was being treated for hypertension and was evaluated for other medical conditions. He could be released as early as Monday.

"Mr. Wei was able to walk into the hospital on his own and without assistance," said Thomas C. Royer, the hospital's chief medical officer. "We are conducting further tests and, in the meantime, we are assisting him in getting much-needed rest."

Wei's relatives and friends have said he suffers from heart problems, high blood pressure and other illnesses that have been aggravated by his long years in prison or labor camps.

Wei, one of China's most eloquent advocates of democracy, has been at the top of a list of political prisoners whose release has been sought by the United States. President Clinton welcomed China's decision to release Wei and said he looks forward to talking to him.

Wei's case was identified as a "top priority" in discussions between Clinton and Chinese President Jiang Zemin during the Chinese leader's state visit to the United States two weeks ago, according to a senior administration official.

The U.S. side had been "pushing hard for four months in the lead-up to the summit" on Wei's case, said the official, who declined to be identified.

"The Chinese understood that we cared very deeply about this case, and that addressing human rights was essential to getting the {U.S.-China} relationship back on track," the official said. Early last week, Chinese Foreign Ministry officials informed U.S. Ambassador to Beijing James R. Sasser that they expected to release Wei on medical parole, but for "some weeks" the Chinese had given "signals" that a release was possible, he said.

In the past, the Chinese have chosen to release dissidents for political reasons. By delaying Wei's release until after the summit, the Chinese government avoided both the risk of Wei overshadowing the state visit and the appearance that China was giving in to Western pressure.

Although Wei's family members said in Beijing that he wanted to return to China, the terms of his release appear to indicate that Wei will not be allowed back into China as a free man. Although Wei had long resisted going into exile, his poor health and harsh prison conditions compelled him to leave, his siblings told reporters in Beijing.

State Department spokeswoman Elaine McDevitt said Washington had been told by the Chinese government that "any decision on Mr. Wei's return to China would be made in accordance with Chinese law." Under Chinese law, Wei is considered a criminal. The State Department official said Wei decided to leave on medical parole, "understanding the Chinese government position."

Wei's brother and sister in Beijing told CNN that Wei signed a document that said if he ever returned to China, he would go straight back to prison. As a result, Wei joins other Chinese dissidents who have been forced into exile in the United States over the last several years. By sending them out of the country, Chinese authorities are able to prevent them from political opposition activity on Chinese soil.

U.S. officials said there is no quid pro quo, explicit or implicit, in Wei's release. However, the senior administration official acknowledged that Wei's release would be "an important factor" for weighing some of China's long-standing requests. Beijing wants to set a date for Clinton's visit to China next year. It wants Washington to drop its annual push in Geneva for a formal condemnation of China's human rights practices by the U.N. Human Rights Commission. And it wants Clinton to lift the remaining sanctions imposed in the wake of the 1989 Chinese Army crackdown on the pro-democracy movement.

Both Jiang and Clinton are scheduled to attend the Asian-Pacific Economic Cooperation (APEC) group summit in Vancouver early next week.

"We have long urged Mr. Wei's release and have had many discussions with the Chinese about his case, including at the highest levels of both governments," McDevitt said today.

"The Chinese government informed us last week that it had decided to grant medical parole for Mr. Wei," she said. When the Chinese government asked whether the United States would be prepared to receive Wei for medical treatment, "we responded positively, took steps to ensure that Mr. Wei would be able to travel to the United States, and helped to arrange for his medical treatment here."

"We have spent an enormous amount of time, the president has himself, encouraging just this action," White House Chief of Staff Erskine B. Bowles said on CBS's "Face the Nation."

Wei was released from a prison about 75 miles from Beijing, where he had been held since being sentenced to 14 years in December 1995 for sedition. Reports of his declining health had prompted repeated requests from his family in recent months for medical parole.

He was taken from the prison Saturday night and allowed to meet for several hours with family members in Beijing this morning before he was put on a nonstop Northwest Airlines flight from Beijing that arrived at Detroit Metropolitan Airport today. He was accompanied on the flight by two officials from the U.S. Embassy in Beijing, a Chinese-speaking political officer and a nurse.

"He is in high spirits because he is the sort of person who is always in good spirits," his brother Wei Xiaotao told Reuters in an interview in Beijing.

"He hopes to have a quiet medical checkup, have a rest and read some books," the brother said. "We did not talk about his future plans. He hopes he will come back one day."

They also said he remained committed to his belief in democracy.

"He is firm and unshakable. No situation would make him give up his pursuit and ideals," Wei's sister, Wei Ling, told the Associated Press. "He thinks the sacrifices he has made for a just cause are worthwhile."

Wei Shanshan, 42, another sister of the dissident, arrived here tonight from Germany. "I'm very happy he's here and safe," the Associated Press quoted her as saying through an interpreter as she walked through the airport carrying her 6-month-old child.

Human rights groups welcomed Wei's release, but said Beijing should release all its political detainees. The New York-based Human Rights Watch said the timing of Wei's release, after the U.S.-China summit and just before Chinese Justice Minister Xiao Yang arrives in Washington Monday for talks with U.S. officials, is consistent with the "hostage politik" that Chinese leaders have pursued since the 1989 Tiananmen Square crackdown.

"When they need to offer a concession for political reasons, they release someone they should never have arrested in the first place," said Sidney Jones, executive director of Human Rights Watch/Asia, in a statement.

Wei's plane was met in Detroit by several Chinese human rights activists and supporters. Among them was Xiao Qiang, executive director of the New York-based exile group Human Rights in China.

"We do not believe that this is a sign of human rights progress in China, because his voice cannot be tolerated in China itself, and thousands of others like Wei Jingsheng, not as known as him, but still equally important, are still held in Chinese prisons," Xiao said.

A Red Guard during the Cultural Revolution and later an electrician at the Beijing Zoo, Wei gained prominence during a short-lived democracy movement in 1979. In an essay, he attacked then-senior leader Deng Xiaoping by name for failing to implement the "fifth modernization," -- democracy -- in addition to the economic reform program known as the "four modernizations." He was arrested one week later, and in October 1979 was sentenced to 15 years in jail.

He was released in September 1993, when Beijing was bidding to host the 2000 Olympics. For six months, Wei helped revitalize the country's feeble dissident movement. But in the spring of 1994, Wei was again detained after meeting John Shattuck, U.S. assistant secretary of state for human rights. Held for 18 months without charge or trial, Wei was brought to court in November 1995, and sentenced a month later to another 14 years for conspiring to subvert the government. Staff writer Terry M. Neal in California contributed to this report. CAPTION: Wei Ling, left, and Wei Xiaotao, siblings of prominent Democracy advocate Wei Jingsheng, meet with journalists in Beijing after their brother left jail. CAPTION: Wei Jingsheng, right, at 1995 trial in Beijing. He was sentenced to 14 years for conspiring to subvert the government but was released and left China over the weekend.