Iran accused the United States early today of adding a surprise document to their hostage release agreement and later threatened to set a deadline for taking "more severe action" if Washington did not start the transfer of Iranian assets to a foreign bank account.

The threat was made before Washington announced that agreement had been reached on all aspects of the negotiations and that banks had been ordered to start moving Iran's frozen assets.

The threat was made by Iranian hostage negotiator Behzad Nabavi, who had issued a statement around 1:30 a.m. Tehran time (about 5 p.m. Monday EST) accusing U.S. banks of "an underhanded maneuver" that delayed the hostages' departure from Iran.

After a long night of further indirect contacts between Tehran and Washington through Algerian intermediaries, Nabavi told the official Iranian radio at around 8 a.m. Tehran time (11:30 p.m. EST Monday) that Iran would set a deadline for transferring the assets after discussing the issue with the Algerian mediators in Tehran.

"We have asked the Algerian delegation for a meeting in which we will give our latest opinions and give a new deadline for American banks to transfer deposits to the Bank of England," Nabavi said, according to Reuter news agency in Tehran. "If this does not take place, obviously we will take more severe action."

Nabavi did not say when the deadline would be or what action Iran would take if it were not met.

The sudden accusation early today stemmed soaring hopes that the hostages at last were on their way out of Iran and put off conclusion of an agreement that Iran's negotiators had defended against critical questioning hours before as a major defeat for "the Great Satan."

According to the official Pars News Agency, which carried Nabavi's charge, he said Algerian intermediaries in Tehran had handed the government on 11-page apendix drafted by American banks to oblige Iran to give up some of its U.S.-held asserts.

Officials in Washington immediately denied that they had sought to dupe the Iranians. These officials portrayed the last-minute difficulty as a purely technical one that could be overcome quickly without reopening negotiations.

Iranian Central Bank Governor Ali Reza Nobari said the problem involved an amendment that would foreclose Iran's right to challenge the amount of its assets held by U.S. banks, but that the matter could be resolved fairly easily by a change in language. By contrast, Nabavi's remarks seemed to reflect a more serious political side of the problem -- fears that the agreement generally might provide ammunition for the government's domestic critics -- and it was not immediately clear whose approach to the issue would prevail.

In an English-language dispatch, Pars said U.S. banks "have meant to make it binding on Iran to drop any further claims beyond the approximately $8 billion . . . to be escrowed in the British central bank." The agency quoted Nabavi as saying this violated the agreement negotiated in Algiers.

The crux of the dispute appeared to be a discrepancy -- long evident in the two sides' public statements -- on the account of Iranian assets frozen by the United States. Nabavi said the agreement announced yesterday acknowledged that Tehran and Washington did not agree on the amount and stipulated that this dispute "would have to be settled through the reciprocal banks of the two countries," Pars said.

The agency quoted Nabavi as saying that the unnamed U.S. banks now claimed that $8 billion was "the whole of the assets credited to Iran" and that the agreement announced Monday contained no such appendix.

Pars said the appendix came "at the 17th hour, which even with the utmost optimism could only be viewed as an underhanded maneuver for delaying the final solution of the problem, especially after the U.S. president had issued an order for releasing Iran's assets in the U.S. banks."

"Nabavi said that the government of the Islamic Republic of Iran severely condemned this subterfuge by the U.S. banks and wishes to open the minds of the world's people and especially the minds of the American public to this fact," Par said.

The chief Iranian hostage negotiator said that under the U.S.-Iranian agreement, the American banks must transfer Iran's assets to the British central bank before the hostages could be freed. As of midnight in Tehran (3:30 p.m. EST Monday), Iran had not received word of this transfer, Nabavi said.

According to Pars, Nabavi "blamed the U.S. banks for needlessly dragging out the issue." He said U.S. officials were negotiating with Algerian intermediaries in Algiers to resolve the problem and that the Algerian government "fully supported Iran's stand."

Nabavi's charges appeared to raise the prospect of a major snag in the last-minute efforts to tie up the loose ends of the agreement, which was announced after weeks of steadily intensifying negotiations among Washington, Tehran and Algiers.

However, the 38-year-old Iranian minister for executive affairs has been known to abruptly change the tone of his statements, which often have been marked by vagueness and subject to varying interpretations.

Nabavi's accusations came after a day of conflicting reports about an imminent end to the 52 captive Americans' 14 1/2-month ordeal. At different times during the day, it was reported that the hostages were about to be flown out of Iran and that technical hitches had developed in setting up an Iranian escrow account in London.

The hitches initially were characterized as relatively minor both in Tehran and Washington, and preparations went ahead at Tehran's Mehrabad International Airport to receive the hostages and get them on their way home.

Two Algerian Boeing 727 jetliners were standing by on the tarmac along with a smaller plane used to bring six Algerian doctors to Tehran Saturday to examine the hostages before their release.

The doctors performed these examinations Monday, and film of the Americans undergoing the check-ups and eating lunch was shown on Iranian television later in the day.

According to Iranian sources' reached by telephone in Tehran, the hostages were not taken to the airport yesterday, but baggage was apparently loaded on one of the Algerian jetliners in preparation for their departure, and security forces around the terminal were strengthened.

These sources said the plan initially was to bring the hostages to the airport and send them off in the early hours of Tuesday Tehran time when the terminal could be more easily cleared.

Later, the Associated Press quoted an airport official as saying in a telephone interview that the aircraft crews had gone back to their hotel and would return Tuesday morning for a planned departure with the hostages at 10 a.m. Tehran time (1:30 a.m. EST). It was not clear, however, whether Nabavi's charges would further postpone this departure time.

Earlier yesterday, Iranian officials had proclaimed the agreement with the United States as a major defeat for "the Great Satan" amid indications of pressures building in Tehran to justify Iranian concessions.

Nabavi hailed the accord as a triumph for Iran at a news conference and on a radio talk show. But the nature of some of the questions from Iranians and the defensiveness of his replies suggested that the Iranian negotiators were under some pressure to fend off potential criticism from domestical political adversaries.

In the morning phone-in show on Tehran radio, Nabavi, tired from the last several days of practically nonstop negotiations, said, "We achieved great victories in occupying the spy nest [U.S. Embassy] and the hostage-taking. I believe, so far as resolving the problem is concerned, there too we achieved a great victory."

However, in the first question, an unidentified listener said, "Certain people believe that you have solved the hostage issue from a position of weakness. They claim that America is holding the trump card."

Nabavi replied that such critics either had "an ulterior motive" or were "unrealistic." He then went on to say, "God willing, once we present the outcome of our work, then everyone will realize that it was not from a position of weakness. Rather, it was from a position of strength and based on victory."

The question appeared to reflect earlier criticism from the camp of President Abol Hassan Bani-Sadr, who has argued that by refusing to allow the hostages' release early last year, his Moslem fundamentalist rivals eventually weakened Iran's position in negotiating on the issue.

The government of Prime Minister Mohammed Ali Rajai, in which Nabavi is minister for executive affairs, also faces a potential backlash from another quarter, the Islamic hard-liners who opposed a settlement of the issue when Iran's Majlis, or parliament, was debating four conditions for the Americans' release.

In an apparent effort to spread the responsibility for the agreement with the United States, Nabavi repeatedly referred to the parliament's authorization for the government to seek a settlement.

In reply to another question on the radio program -- on whether one of the morning newspaper headlines, "America Surrenders to Iran," was really true -- Nabavi said, "We managed to rub the nose of the biggest world oppressor and superpower into the dust, thus forcing it to submit to the demands made in our Majlis ratification."

Later, in an afternoon news conference, Nabavi outlined the agreement in terms suggesting that Iran had wrung major concessions from Washington. However, asking about the lack of explicit provisions in the agreement for return of the shah's wealth -- originally a major Iranian condition -- Nabavi said it was "the principle that matters."

Another Iranian questioner put Nabavi on the spot by asking if he would personally take responsibility for the agreement if there were any public criticism of it. Nabavi replied that both he and the government stood behind everything in the accord.