CAIRO, AUG. 26 -- The United Nations announced today that Secretary General Javier Perez de Cuellar will meet Thursday in Jordan with Iraq's foreign minister to discuss the Persian Gulf crisis.

Also today, Iraq allowed 52 Americans to leave the country but continued to round up Westerners.

The announcement marked the first formal attempt by the U.N. leader to mediate in the international dispute sparked by Iraq's Aug. 2 invasion of Kuwait and its detention of thousands of Westerners.

U.S. national security adviser Brent Scowcroft said on ABC today that the Bush administration "would have no problem" with a mediation effort by Perez de Cuellar but made clear that the only thing the United States is ready to negotiate now would be "the timetable, the modalities" of an Iraqi withdrawal from Kuwait.

Iraqi leader Saddam Hussein, who has called for talks with the nations arrayed against him, has declared that his conquest of Kuwait is irreversible. But Iraqi Foreign Minister Tariq Aziz told Cable News Network today: "We are open to listen to suggestions. We have not closed the door to any idea, but this question is complicated by the American threat to Iraq."

In the Persian Gulf, U.S. warships shadowed a number of Iraqi vessels but did not exercise their new authority, granted Saturday by the U.N. Security Council, to use force to maintain a worldwide trade embargo against Iraq.

Soviet Foreign Minister Eduard Shevardnadze said today that Moscow will not use force in the gulf -- where an international armada of warships is deploying -- despite voting for the U.N. resolution. At a news conference with visiting French Foreign Minister Roland Dumas, Shevardnadze said that while Moscow will not object if other countries, including the United States, use military means to back up the embargo, "we have no such plans to use force or take part in such an operation."

In Baghdad, Iraq today allowed 55 women and children -- family members of State Department employees who had been stationed at the U.S. Embassy in Kuwait -- to travel in an automobile convoy from Baghdad to Turkey. When the convoy reached the border, however, only 52 were allowed to cross into Turkey, while three young men -- described by a State Department spokesman as dependents of U.S. diplomats -- were kept in Iraq and returned to Baghdad. It was not clear why the three were turned back.

Iraq also denied permission to 54 diplomats from the U.S. Embassy in Kuwait to leave Baghdad, where they are now working with officials at the U.S. Embassy in the Iraqi capital to help stranded Americans, according to Robert M. Kimmitt, undersecretary of state for political affairs, who appeared on a CBS interview program. There are an estimated 3,000 Americans trapped in Kuwait and Iraq.

Iraqi officials, in ordering foreign embassies in Kuwait to close and relocate to Baghdad, initially had promised that employees of the U.S. Embassy in Kuwait who went to the Iraqi capital would be allowed to leave. But they later reneged, saying the diplomats had lost their diplomatic status and would be detained along with other foreigners.

In Kuwait, diplomats at about 25 foreign embassies continued to defy Iraqi orders to close. Some of the facilities remained guarded by Iraqi troops and deprived of electricity, water and telephone services.

U.S. Ambassador W. Nathaniel Howell and seven other diplomats remained inside the American Embassy, which has had its power and outside water supply cut off and is surrounded by Iraqi soldiers. Scowcroft said the Iraqis have not tried to enter the U.S. Embassy by force, although he said he had received reports that soldiers had forcibly entered China's embassy in Kuwait.

The American ambassador and the other diplomats have enough food and water to last "a matter of weeks," John Kelly, assistant secretary of state for Near Eastern and south Asian affairs, said today on NBC. "Their morale is good. They're holding fast and doing fine."

But the United States, Britain and France all reported more of their citizens in Kuwait being rounded up by the Iraqis, who are placing many of the hostages at strategic locations around Iraq to use as human shields against U.S. attack.

"We've had various reports of people being held at hydroelectric installations, power plants, military facilities around Iraq," Kelly said. "But it is hard to know where the people are."

The French Foreign Ministry said today that eight more French nationals were taken from Kuwaiti hotels, bringing to at least 33 the number of French in Kuwait who have been moved to undisclosed locations by Iraqi troops. The British Foreign Office said eight more Britons had been rounded up, raising to 147 the number of Britons taken into Iraqi custody. And the State Department confirmed that at least two more Americans had been picked up by Iraqi troops this weekend in Kuwait.

U.S. officials, who today ordered 50 additional Army reserve and National Guard units in 25 states to report for active duty in the gulf region, said their strategy of isolating Iraq economically and politically was in place and they hoped it would end the crisis. "I think it's time now to see whether or not it will work," Scowcroft said on ABC.

Scowcroft also confirmed that the United States, which has already deployed at least 40,000 troops in Saudi Arabia, will offer asylum to Iraqi sailors who "respond peacefully" to efforts in the gulf to prevent supplies moving to and from Iraq.

Kelly said Iraq is already being affected by the trade sanctions. "We know that internal food prices are going through the roof for certain commodities like rice, sugar and so on," he said. "We know that there are bread lines."

The Iraqi ambassador to the United States, Mohamed Sadiq Mashat, acknowledged on CBS that the sanctions "definitely" will affect his country. "But," he added, "we are people with lots of pride and we are going to resist and we are going to give sacrifices. We will tighten our belt to defend our own country."

The exodus of foreigners from Iraq and Kuwait into Jordan swelled today, with about 10,000 people -- most of them Arabs and Asians -- arriving at the dusty border post of Ruweished by mid-afternoon.

International relief workers toiled around the clock to ferry in supplies to Jordan, where 220,000 refugees have poured in since Iraq opened its border Aug. 7, Jordanian officials said. Turkey, too, has received thousands of refugees and has threatened to close its border.

The government of Iran, which has promised to abide by U.N. trade sanctions against Iraq, today announced that foreigners fleeing Iraq and Kuwait can do so through Iranian territory. Tehran radio quoted Foreign Minister Ali Akbar Velayati as saying that Iran, which shares a 730-mile-long border with Iraq, was changing its policy for humanitarian reasons. On Saturday, Syria also opened its border to fleeing foreigners.

In a related development, Iran confirmed that Iraq had freed 600 Iranian prisoners of war today. Earlier, Baghdad had said all Iranian POWs had been repatriated. The move resulted from an initiative this month by Saddam to end his dispute with Iran in order to free up troops deployed on the Iranian border.

But Gen. Slavko Jovic, the commander of U.N. soldiers monitoring the cease-fire that ended the Iran-Iraq war in 1988, was quoted by Tehran radio as saying that Iraqi forces still occupy pockets of Iranian territory and that he was planning to pursue the issue with Baghdad.

A U.N. spokesman said Perez de Cuellar's mediation effort, which will begin Thursday in Amman, Jordan, with his meeting with Aziz, was launched by the secretary general in hopes that he could "start diplomatic efforts aimed at solving in all its aspects the critical situation in the gulf area."

But Prime Minister Margaret Thatcher of Britain, which has thousands of citizens being held by Iraq, ruled out negotiations with Saddam, saying there should be no talks with "a tyrant."

"There is no negotiation with a person who by force has taken someone else's country," she said today after prayers near her country retreat at Chequers.

The U.N. initiative came amid a flurry of diplomatic activity in the Arab world, led by Jordan's King Hussein and Sudanese leader Omar Bashir. As Hussein, who has expressed sympathy for Saddam, flew to Libya on the first leg of a new diplomatic shuttle, Bashir and two senior Libyan envoys flew to Baghdad from Amman.

"We are moving in an attempt to pluck out the fuse of war. . . . We are trying to crystalize an Arab initiative," Bashir said during a stopover in Amman.

The Arab League, continuing to show discord over how to respond to Iraq's invasion and annexation of Kuwait, has been unable so far to muster a quorum for an emergency meeting of its foreign ministers later this week.

The meeting was originally planned for today, but was postponed until Thursday because of difficulties in getting the required majority of the 21 member states to send their foreign ministers to Cairo.

The meeting is viewed by some analysts as an important element of Egypt's strategy of keeping diplomatic pressure on Iraq and preventing Saddam from diverting attention from the central issue of the unacceptability of any nation seizing the territory of another by force.

Egyptian Foreign Minister Esmat Abdel-Meguid today said he had "hopes" that a quorum can be attained in time for the Arab League foreign ministers' meeting, which was called by the league's secretary general, Chedli Klebi, to discuss the status of an all-Arab military force that has been sent to Saudia Arabia to help the kingdom defend itself against a possible Iraqi attack.

Abdel-Meguid said 10 ministers had confirmed that they would attend. He said he expected more to accept "very soon."

The all-Arab force was approved during a stormy Arab summit in Cairo Aug. 10, during which the emir of Kuwait, Sheik Jabir Ahmed Sabah, walked out and at which the Iraqi and Kuwaiti delegations were reported to have thrown food at each other. Immediately after the invasion, the league's foreign ministers met and 14 voted to condemn Iraq.

Shortly before leaving today on a visit to Moscow, Abdel-Meguid said he hoped that those resolutions, coupled with the U.N. Security Council's approval of the use of force to stop embargo violations, "will have the impact of making Iraq believe that the whole international community is united against the aggression."

He did not provide any explanation for the difficulty in attaining the quorum for another Arab League meeting or assess what effect a failure to convene the session would have on Arab unity.

Responding to a question at a news conference, however, Abdel-Meguid said that some of Saddam's recent public offers to negotiate may be cause for guarded optimism that talks for a peaceful resolution of the conflict are possible.

"I have sensed it in some of his recent statements. It will be a very encouraging step if he follows it up," Abdel-Meguid said. But he added, "It is a time to see facts. . . . We need to see some very concrete action."

Staff writer Susan Okie in Washington contributed to this report.