A chartered twin jet Grumman Gulstream taxied to a stop at a remote corner of New York's LaGuardia Airport late on the night of Oct. 22, and a guant man, accompained by his wife, a dozen aides and two Doberman pinschers, descended slowly and shuffled unsteadily to a waiting limousine.

The 12-car motorcade, under heavy guard, rolled across town to New York Hospital -- Cornell Medical Center, the latest temporary resting place for the deposed shah of Iran, Mohammad Reza Pahlavi, once one of the world's most powerful men and still one of the richest.

The arrival of the shah in the United States on medical grounds was in one sense the final act in a mostly hidden process of policy-making and jockeying in Washington and several other capitals since Pahlavi's forced departure from Iran last Jan. 16. But in another and more realistic sense, the entry of this man, who arouses such fierce and conflicting emotions, was only the beginning.

Like a fuel rod entering an atomic core, the arrival of the shah three weeks ago tomorrow initiated a powerful chain reaction: First, in Iran, the occupation of the U.S. Embassy, the capture of 61 American diplomats, clerks and Marine guards as hostages and the replacement of a relatively moderate and modernistic government by unalloyed theocratic rule. Then, in the United States, a passionate response of anger and humiliation -- checked only by concern for the lives of the hostages -- that is likely to generate grave repercussions in national politics and international action.

In Tehran today, the American hostages are pawns in a contest of wills over the person and future of the 60-year-old former monarch. The militant student captors and the approving regime of Ayatollah Ruhollah Khomeini formally demand the return of the shah for trail as a war criminal, and Iranian diplomats informally suggest transfer of the shah from the United States to almost any other country as a means of settling the crisis.

The militants' demand is highly popular in Iran, where both the fundamentalist and radical branches of the revolution that toppled the shah see his rule as bloody, corrupt and illegitimately imposed and maintained by the United States.

In Washington, the formal demand -- and its informal alternative -- are seen as a barbaric breach of both ethics and international law, totally unacceptable. To even consider handing over or sending away a sick man who was a major U.S. ally for 37 years is seen in high circles as a craven act of submission to blackmail, outside the pale of U.S. tradition as well as U.S. fundamental interests.

A statement issued by a spokesman for the shah in New York last Thursday said he had "expressed his willingness" to leave the United States in hopes of gaining the freedom of the hostages, but that his doctors "remain adamant" that such a move now would involve a risk to his life. The statement said further surgery involving his gallstones is planned in three weeks, suggesting that no move by the shah is contemplated before that time.

Appalling as the prospect is, there is a substantial body of opinion within the government that Khomeini may follow his characteristic unyielding pattern of behavior and refuse to authorize release of the U.S. hostages until the shah leaves the United States. Such a long-running international crisis would be almost unbearable to the American government, increasing the prospect of a fierce response sooner or later.

The worldwide wanderings of the once powerful Shahanshah Aryamehr, "kings of kings, light of the Aryans, began with his departure from Tehran Jan. 16. The United States made it clear that he was welcome here, and President Carter said publicly the next day that the deposed ruler "will later come to our own country."

The shah, reportedly hoping he could soon return to Iran, chose to go initially to the Third World countries of Egypt and Morocco rather than travel the physical and political distance involved in taking up residence in the United States. By mid-March, as it became increasingly clear that a return to power was out of the question, the shah came under pressure from King Hassan of Morocco to move on -- but by now the United States was having strong doubts.

By March the exiled Khomeini had returned to Iran in triumph, the interim Bakhtiar government had fallen and the anti-shah revolution had taken control of government offices and revolutionary tribunals, as well as the streets.

The United States, after a round of policy deliberatons, decided to maintain whatever ties were possible with the new regime because of its strategic location between the Soviet Union and the Middle East, its petroleum resources and historic U.S. interests there. It was clear that allowing the shah into the United States would make links to the new Iran extremely difficult, if not impossible.

Carter decided, after debate within and outside the administration, that the shah should be informed he was not welcome in the United States under the circumstances. Former secretary of state Henry A. Kissinger and Board Chairman David Rockefeller of the Chase Manhattan Bank, who had been sponsoring the shah's admission here, angrily rejected a government entreaty that they pass the disappointing word to their old friend.

Kissinger, in telephone calls to the president and national security affairs adviser Zbigniew Brzezinski and in a private meeting with Secretary of State Cyrus R. Vance, reportedly argued it would be "dishonorable" to reject the shah. The government, however, was concerned even then aboutt an effort to seize Americans in Iran as hostages in a demand for extradition of the shah if he came here.

Having lost the battle in Washington, Rockefeller arranged for the shah to take up temporary residence in the Bahamas. Later Rockfeller and Kissinger intervened with Mexican President Lopez Portillo to arrange for the shah to move to a luxurious estate south of Mexico City.

Kissinger, Rockefeller and New York attorney John J. McCloy, often considered the patriarch of the traditional foreign policy establishment, formed an unofficial committee of three to continue pushing for the shah's admission here.

Kissinger went public in early April with a quotable declaration at a Harvard Business School dinner that "a man who for 37 years was a friend of the United States should not be treated like a Flying Dutchman who cannot find a port of call." Every few weeks he would make another such statement to keep the subject alive and the pressure on the government.

Meanwhile, counterpressures began to build up in Iran. In April, the Iranian government warned Mexico, without success, that bilateral realtions could be affected if the shah were permitted to go there. On April 23, Iran warned Washington by diplomatic note that any visa or asylum for the shah in the United States would be considered "an unfriendly act" and would have an adverse effect on relations. A number of other, less official statements of the same sort came from the Iranian government.

The shah moved to Mexico June 10 for what was clearly understood to be a temporary stay. By mid-summer the pressures on U.S. officialdom began to mount again. Former president Richard Nixon visited the shah in Mexico in mid-July, Kissinger and Rockefeller continued their appeals.

According to classified documents released last week by Iranian students occupying the U.S. Embassy and not seriously disputed by American officials, Vance sent a message July 26 reporting that the shah could remain in Mexico "at least until October" and that his coming to the United States was again a sensitive issue in Washington.

The embassy was asked, according to the documents, its assessment of the effect the entry of the shah might have "on the well-being and security of the American residents in Iran and especially the American employes of the embassy and the relations between us and the Iranian government."

U.S. Acting Ambassador L. Bruce Alingen replied, according to another purloined document, with suggested ways of presenting the shah's eventual entry to a stabilized Iranian government.

Laingen's memo also said that fear remained that Americans could be taken as hostages in retaliation. "We should not take any steps in the direction of admitting the shah until such time as we have been able to prepare an effective and essential force for the protection of the embassy," according to the memo.

Once again, Washington's decision was to put off admitting the shah. Vance said publicly Sept. 27, in response to a question from another New York establishment figure, Foreign Affairs magazine editor William P. Bundy, that "we have had to take into account the possible dangers to American people [in Iran] at this time" and that therefore the shah's admission would not be in the U.S. national interest.

According to one account, it was clear from the beginning that the shah eventually would be permitted to come here, in keeping with U.S. tradition. The only debate was over timing and tactics. Others dealing with the matter said they know nothing of a formal decision in principle, though the shah's admission was described as a continuing option.

What changed the picture suddenly and decisively was word from the shah's Mexico entourage, received by the State Department in the third week of October, that the shah had become jaundiced, feverish and very ill. Rockfeller arranged for a New York specialist in tropical medicine, Dr. Benjamin H. Kean, to fly to Mexico to examine Pahlavi.

The medical report, dated Oct. 20, told of "enlarged neck glands, increasing abdominal distress as well as deepening jaundice." there was a suspicion of both gall bladder disorders and of cancer of the lymph glands.

"Highly technical studies" to diagnose the possible cancer "cannot be carried out in any of the medical facilities in Mexico," the report said.

The shah's entourage told the doctors, and later announced publicly, that Pahlavi had suffered from lymph gland cancer for about six years. This was a complete surprise to U.S. intelligence as well as to State Department officials, one of whom admitted to being "dumbfounded" by the news.

According to an official dealing with the diplomatic problem, the government accepted the word of Dr. Kean, who is on the staff of New York Hospital, that this facility was the best place for Pahlavi's treatment. So far as can be determined, no alternative facilities either in the United States or abroad were investigated. No government physician examined the shah.

To turn down a request for admittance of the shah in the face of medical findings, including possible cancer, would have placed the Carter administration in a politically untenable position at home. But even as they prepared to receive him, officials took steps to defuse the inevitable Iranian reaction.

Henry Precht, the State Department's director of Iranian affairs, flew to Tehran. On Oct. 21, accompanied by Laingen, he informed Prime Minister Mehdi Bazargan and Foreign Minister Ibrahim Yazdi of the shah's condition and told them that his entry to the United States was being considered seriously. Precht was told, according to Iranian sources, that the Shah's entry was "not acceptable" to the Iranian government and people and would have undersirable consequences.

The next day, the U.S. diplomats informed the Iranians that the shah would arrive in New York that night. Tehran repeated its protest, and the United States was asked to permit Iranian doctors to assure themselves of this emergency situation by examining the patient and his medical records.

Behind the diplomatic language was the deeply held fear of Bazargan and Yazdi that the strong emotions loosed by the shah's arrival in the United States would undermine the position of the moderate forces. The effort to provide convincing medical evidence was intended to head off an eruption.

Informed of what was being done. Khomeini's first public reaction was relatively mild: The United States has accepted the shah "under the pretext" that he is suffering from cancer. "Inshallah [God willing], it is true."

The Iranians named two physicians living in the United States to examine the shah, but this proposal was rejected in official Washington. Neither were the doctors permitted to see the shah's medical records, but instead were given a summary statement of little more than a page, plus a copy of the New York Hospital press release.

On Oct. 30, the Iranian government protested the failure to provide detailed medical information, and on Nov. 1 it again formally rejected the U.S. admission of the shah in a diplomatic note that called for his deportation.

Anti-shah and anti-American emotion, now explicitly encouraged by Khomeini, flared in Iran. The furor was based in part on a fear that now seems irrational to Americans -- that the United States is preparing to bring the shah to power once again, as the Central Intelligence Agency did in [word illegible]

On Sunday, Nov. 4, one week ago and 13 days after the shah's arrival in New York, militant students swarmed into the American Embassy and took 61 hostages. The police authority of Iran, whoever controlled it at that moment, did not raise a finger to stop the powerful and unprecedented reaction.