President Bush yesterday ordered U.S. military aircraft and troops to Saudi Arabia after King Fahd approved the deployment of a multinational force to defend his oil-rich nation against the growing Iraqi invasion force massed near the Saudi border with Kuwait, administration officials said.

Egyptian armed forces were preparing to join the deployment, American officials said, and the Bush administration was pressing other moderate Arab states to follow suit.

Western powers were organizing a multinational naval armada to blockade Iraq's ports and oil pipeline terminals if that is needed to enforce the total trade ban against Iraq approved by the United Nations Security Council Monday. The British have agreed to cooperate with a naval blockade if it becomes necessary, and France is moving ships to the region and may also join. Soviet ships are already in the area, U.S. officials said, and there have been informal discussions on possible Soviet participation in the armada.

Yesterday afternoon the White House declared that Saudi Arabia was under "imminent threat" from the "offensive posture" of tens of thousands of Iraqi soldiers. The White House began notifying congressional leaders yesterday that American troops and aircraft were being sent but made no public statement. Bush is scheduled to address to the nation at 9 a.m. today, and officials familiar with the content of his speech said it will stress the involvement of the Soviet Union in the multinational force.

U.S. intelligence officials expressed concern over signs that the Iraqis were loading chemical bombs on aircraft and ground vehicles that could deliver them in a new assault.

U.S. intelligence reports indicate that Iraq has almost doubled the number of tanks in Kuwait to 500 since the initial invasion Thursday and is preparing to add 300 more. The number of Iraqi troops in Kuwait has expanded to about 120,000, and more are being mobilized inside Iraq, officials said.

The initial U.S. deployment to Saudi Arabia, military officials said, included about 2,300 troops in the division ready brigade of the 82nd Airborne Division from Fort Bragg, N.C.; 48 F-15 fighters in two squadrons from the 1st Tactical Fighter Wing at Langley Air Force Base, Va.; six to eight B-52 bombers based in the United States; and a full headquarters contingent of the U.S. Central Command, normally based in Tampa, with its related intelligence and support personnel. The troops will be used to provide security for American aircraft stationed at Saudi air bases, officials said.

U.S. officials said F-117 Stealth fighters could also be used against some Iraqi targets if they are needed to slip past Iraqi air defense radar. Several officials said they already had been deployed to the region.

Turkey yesterday effectively shut off the two pipelines that carry Iraqi oil across its territory to the Mediterranean. Iraq itself slowed to a trickle the flow of oil through its pipelines that pass through Saudi territory to the Red Sea, apparently because it had no customers for it.

The Persian Gulf crisis began last Thursday when Iraqi President Saddam Hussein sent more than 100,000 troops into Kuwait, quickly conquering the country. Saddam's advance against his neighbor and his quest to dominate the Persian Gulf have provoked a historic mobilization of the industrial West, the Soviet Union, Japan and some Arab states to confront Iraq with economic sanctions. Yesterday's moves added military muscle to the confrontation.

Egypt's contribution to the multinational force will consist of about 2,000 airborne soldiers plus additional ranger and armored units, U.S. officials said. That force was waiting to be transported to Saudi Arabia yesterday, perhaps by American aircraft, the officials said. In Cairo, an Egyptian defense ministry official denied that Egyptian troops were being sent to Saudi Arabia.

Egyptian President Hosni Mubarak was said by U.S. military sources here to have agreed to send troops if required to help defend Saudi Arabia. In a meeting with Defense Secretary Richard B. Cheney yesterday, Mubarak also approved the passage through the Suez Canal of the nuclear-powered aircraft carrier USS Dwight D. Eisenhower and several escort ships. Mubarak insisted that they transit the canal at night.

After two days of talks with King Fahd, which brought Saudi approval for the U.S. deployment, Cheney spent yesterday in Cairo and then flew on to Morocco for consultations with King Hassan II. Officials here said Cheney was seeking Moroccan support for the multinational force in Saudi Arabia.

After his meetings with Cheney, the Saudi monarch "agreed to everything we asked," one knowledgeable source said.

Saudi Arabia has deployed tanks and some infantry forces nearer to its frontier with Kuwait, but they are vastly outnumbered by the battle-hardened Iraqis who would be opposing them.

The Saudi government also has evacuated a number of oil workers from the region near the border.

The White House gave only an indirect explanation yesterday of why Bush had no public comment on the U.S. deployment. White House spokesman Marlin Fitzwater said that for "very strategic and valid reasons I cannot comment in any way" on the deployment of U.S. forces. "I can tell you someday and it will all make sense," he added. "We have to be very careful in this situation . . . but I think the American people have a very good idea of exactly what's happening."

Fitzwater quoted Bush as telling a Cabinet meeting yesterday that the growing Iraqi threat to Saudi Arabia constituted "a threat to United States security interests."

Rep. Les Aspin (D-Wis.), chairman of the House Armed Services Committee, said he supported "this military action we're taking."

"It is essentially a preventative move on our part," he continued, "to ensure {Saddam} Hussein doesn't attack Saudi Arabian oil fields."

The White House began contacting congressional leaders early yesterday morning. Senate Minority Leader Robert J. Dole (R-Kan.) spoke with Bush at about 9 a.m. and said he was asked not to discuss the conversation. House Speaker Thomas S. Foley (D-Wash.) also received a call from Bush and refused to comment on it. National security adviser Brent Scowcroft telephoned Senate Majority Leader George J. Mitchell (D-Maine), who likewise was guarded about the discussion afterwards.

While Bush was silent, Vice President Quayle, traveling in Venezuela, called Saddam an "outlaw" and added, "I can tell you this, President Bush and others are adamant that Saddam Hussein not achieve victory. They are adamant that he implement an unconditional withdrawal."

Both the White House and State Department refused to discuss the two-hour encounter Monday between U.S. Charge d'Affaires Joseph C. Wilson and Saddam in Baghdad. Fitzwater yesterday characterized it as "very difficult . . . very negative" and added that Saddam showed "no intention of leaving Kuwait and had every intention of staying and claiming it as his own."

Iraq yesterday denied a report in yesterday's Washington Post that Saddam threatened to attack Saudi Arabia if the kingdom shut down two Iraqi crude oil pipelines under the terms of the U.N. trade embargo. The Iraqi news agency, citing the Post report, termed it "ill-intentioned and . . . meant for intrigue {and} to create disorder and divide the ranks."

Administration officials said yesterday that Saddam's threats against Saudi Arabia were blunt and direct, but he did not use the word "attack." Rather, Saddam told the U.S. envoy that if the Saudis either increased their production to help the West or cut off Iraq's oil lifelines, they would be "an enemy of the Arab people and will be dealt with."

Military officials said the Pentagon has dispatched aerial refueling tankers, airborne warning and control system (AWACS) aircraft and special forces teams including the Navy SEALs (Sea-Air-Land units) into the gulf region, and sent prepositioned ships loaded with supplies and ammunition steaming from the island of Diego Garcia in the Indian Ocean.

In the event of an Iraqi attack against Saudi Arabia, officials said, the United States would respond primarily with air power.

The aircraft also could be used to attack strategic sites within Iraq.

Bush also was said to have under discussion using his emergency powers to sell or transfer dozens of F-15s and F-16s to Saudi Arabia to fill out its inventory. Earlier attempts by the Reagan administration to transfer more F-15s to the Saudi air force were blocked in Congress by pro-Israel forces concerned that Saudi Arabia would gain a sophisticated ground-attack capability that might someday be used against the Jewish state.

The immediate deployment of U.S. forces recommended by military leaders to Bush includes other elements of the 18th Airborne Corps and a Marine unit. The other units include a brigade of the 24th Infantry from Fort Stewart, Ga., additional major portions of the 82nd Airborne from Fort Bragg, and the 7th Marine Amphibious Force from Camp Pendleton, Calif.

Major elements of the 82nd Airborne will be flown in C-141 Air Force transports while the Marines will go by fast sealift ships from Jacksonville, Fla., Norfolk and an undisclosed port in the Gulf of Mexico, according to military sources. Nine floating warehouses, called Maritime Preposition Ships -- five from Diego Garcia and four from Guam -- are expected to steam toward the Persian Gulf with war supplies for the Marines.

Troops from the 24th Infantry will be sent by fast cargo ship, a voyage that will take several weeks. Their equipment includes tanks and other armored vehicles.

To broaden the surveillance of Iraqi military activities on the border between Kuwait and Saudi Arabia, military officials said that three Air Force AWACS were to be flown from Tinker Air Force Base, Okla., to join the Saudi surveillance force at Riyadh.

Military planners said last night that the buildup of U.S. and other forces is designed to compell Saddam to back down and withdraw from Kuwait, not to engage in combat anytime soon.

Staff writers Dan Balz and George C. Wilson contributed to this report.