Bowing to congressional pressure, the White House disclosed last night it will seek congressional approval next week for a "significantly" pared-down, immediate arms sale to Saudi Arabia, to be followed by a second request in January to meet the longer-term military needs of the desert kingdom.

The decision to split the arms package into two parts came after discussions with key congressional leaders, who objected to the original $21 billion size of the Saudi proposal that the Defense Department had circulated on Capitol Hill. Saudi officials, during a lengthy White House meeting yesterday afternoon, agreed to the two-track approach, officials said.

An informed source said the sale, which is subject to congressional approval, would be "around" $10 billion. White House and State Department officials said, however, that the exact cost of the package and its components were being determined this weekend. "It could be less than $10 billion," said one official, "it could be slightly more."

The arms sale decision came as Iraq expelled three Americans assigned to the U.S. Embassy in Baghdad, and the United States retaliated by expelling three Iraqis from their embassy here. In both cases, those ordered to leave were the embassy military attache and two civilian diplomats.

The State Department also announced that Secretary of State James A. Baker III will represent the United States at a special foreign-minister-level meeting of the United Nations Security Council in New York on Tuesday to consider the Persian Gulf crisis. Chairing the meeting will be Soviet Foreign Minister Eduard Shevardnadze, whose country now holds the rotating monthly chairmanship of the 15-nation council.

Here in Washington, the governments of the United States and Britain agreed that British troops to be deployed in Saudi Arabia will be directed by U.S. officers at the tactical level, in what officials of both countries say is the first major accord on the chain of command for the multinational forces being assembled in the region.

Tensions remained high in the region, with U.S. officials confirming reports that Saudi Arabia has shut off its oil supply to Jordan. In addition, Baghdad announced that two warplanes "coming from Saudi Arabia's direction" had violated Iraqi airspace. This was the second such alleged incident since the start of the massive U.S.-led military buildup in Saudi Arabia to shield it in the wake of Iraq's Aug. 2 invasion of Kuwait.

An Iraqi spokesman did not identify the aircraft, which he said penetrated Iraqi airspace around midday local time Thursday in the Iraqi-Jordanian-Saudi border triangle area. The news caused panic in the oil market and forecasts of soaring oil prices of up to $65 a barrel if a shooting war breaks out in the gulf.

The surprise halt in Saudi oil supplies to Jordan came barely a month after the Saudi government agreed to pump oil to Jordan to offset losses from the imposition of sanctions against Iraq. Riyadh's explanation was that Jordan has not paid $48 million in oil import dues.

The White House statement on the Saudi arms package contained no details of the components or costs. "The specific items to be provided in the first phase are still being determined and will encompass equipment and training requiring early action," the statement said. "Those items that do not require expedited review will be submitted to the Congress early in the new year."

The statement said the arms sale was "essential" to Saudi Arabia's ability to defend itself against aggression and amounts to a "key dimension of our overall strategy toward the Persian Gulf {that} could serve as well to protect American lives."

U.S. and Saudi officials indicated that the new arms package would reflect congressional concerns that only a portion of the weapons desired by the Saudis can be transferred quickly enough to be used in coming months to defend against Iraqi aggression.

An official said the package was hammered out after a day of meetings and contacts between senior administration officials and Saudi Ambassador Prince Bandar bin Sultan and will include weapons needed "now and in the immediate future" by the Saudi kingdom.

Bandar confirmed in a telephone interview last evening that the two countries had reached a "consensus" and said he was "very happy" with the outcome but declined to provide details. Indicating that he accepted the idea of purchasing the arms in several phases, Bandar said his country was still rethinking "the entire structure of our forces" in light of the Iraqi invasion.

"It is a major event, but not the {immediate} priority," he said of the restructuring, because of the more pressing task of preparing adequate defenses against the estimated 170,000 Iraqi troops now in Kuwait.

The "chain of command" agreement reached by Secretary of Defense Richard B. Cheney and British Defense Minister Tom King is intended to aid future joint military exercises, or if needed, the use of force to defend U.S. and allied interests in the gulf, officials said.

Under the arrangement, the tactical deployment of British forces will be directed by U.S. commanders, while a senior British official will participate in the overall command structure being established by the United States. Responsibility for overall military strategy evidently will continue to be shared by the U.S. and Saudi governments, while Arab forces will be directed by a separate chain of command or by individual nations.

President Bush and other U.S. officials have publicly said "command" questions associated with the growing military deployment have largely been resolved and will not be a hindrance in responding to Iraqi aggression. But U.S. and foreign officials said yesterday that negotiations are continuing.

An agreement similar to the U.S.-British accord "would very likely be satisfactory to us," said Canadian External Affairs Minister Joe Clark in an interview with The Washington Post yesterday. But "that has not been worked out," and in the meantime three Canadian naval vessels and 18 fighter aircraft being sent to the gulf will remain under Canadian command, he said.

A French force of 5,000 troops being sent to Saudi Arabia around Oct. 1 also will remain entirely under French control, according to a statement in Paris on Thursday by Defense Minister Jean-Pierre Chevenement.

King said in Washington that two meetings were held last week to try to agree on a command structure among those nations participating in the naval blockade of shipping destined for Iraq, but he was uncertain if any agreement had been reached. Other officials said the naval forces of each nation remained responsible for different sectors of the gulf waters and are operating only under loose U.S. coordination.

The latest U.S. retaliatory move against Iraqi diplomats followed the expulsion on Aug. 26 of 36 Iraqi Embassy personnel and the imposition of tight travel restrictions on those remaining here.

The special Security Council meeting on Tuesday will be the first time that member countries are represented by their foreign ministers since a 1985 session marking the United Nations' 40th anniversary.

The idea of an aerial embargo to complement the shipping ban in force is under debate at the United Nations. However, U.S. officials and other diplomats said yesterday that it is unlikely to be put to a vote while the Iraqis still are allowing some third-country women and children to leave Iraq and Kuwait on charter flights. An air embargo at this time, the sources said, might provoke Iraqi President Saddam Hussein to halt further evacuation flights.

Staff writers John M. Goshko in Washington and Nora Boustany in Amman, Jordan, contributed to this report.