In response to the dispatch of U.S. forces to Saudi Arabia, Iraq's military occupation force in Kuwait has intensified construction of a strong defensive line of earthen barriers and antiaircraft batteries to protect against attack, U.S. officials said yesterday.

"We see the Iraqi military consolidating its forces in Kuwait," Pentagon spokesman Pete Williams said at a news conference. "They seem to be in a defensive posture, but nonetheless Iraqi forces are still capable of offensive action and . . . more Iraqi military units appear to be heading south from Iraq into Kuwait."

Another senior administration official said the Iraqis no longer are in positions "preparatory to an attack." U.S. forces in Saudi Arabia would have about 24 hours' warning of an attack, the official said, because U.S. intelligence assets are tightly focused on the logistical movements and communications of the estimated 120,000-man Iraqi force in Kuwait.

The Iraqi defensive buildup has occurred over the last two days, administration officials said. It has included the movement of surface-to-surface missiles into Kuwait from Iraq, along with air defense radars and various antiaircraft systems, including Soviet-made surface-to-air missiles.

As U.S. troops took up station on Saudi soil for the first time, the Bush administration was working on multiple fronts to build multinational forces both from the Arab world and from the industrial countries to join the defense of the Persian Gulf and its flow of oil. The Pentagon has code-named the operation Desert Shield.

Britain announced yesterday it will send two squadrons of warplanes to Saudi Arabia, and a fleet of coastal patrol vessels to gulf waters. Meanwhile, France announced it would send an aircraft carrier to join its other vessels dispatched to the region, and would deploy air de- fense forces to Saudi Arabia. Australia was reported close to announcing that it will send a contingent to join the multinational force in Saudi Arabia.

Decisions by Arab nations on whether to commit their forces to the defense of Saudi Arabia awaited the outcome of a meeting of Arab leaders in Cairo, but a senior U.S. official in Washington expressed confidence yesterday that an Arab force would materialize. Paul D. Wolfowitz, undersecretary of state for policy, and Richard A. Clarke, assistant secretary of state for political-military affairs, continued their mission in the region, traveling from capital to capital to encourage Arab participation in the multinational force.

State Department and Pentagon working groups were drawing up options to enforce the total trade ban against Iraq.

The United States, which has moved a naval armada to waters off the Arabian peninsula, has not yet begun a blockade of oil and food shipments in and out of Iraq, but senior officials here said that military planning for such a blockade was proceeding.

These officials indicated yesterday that a U.S. decision to impose a blockade would be affected by the pace of diplomacy at the United Nations and by the efforts made by Iraq to circumvent the worldwide trade embargo voted against it Monday by the U.N. Security Council.

One senior administration official said that as time passes, some countries or traders will increasingly be tempted to cheat on the embargo and either buy oil from Iraq or sell it food and other commodities. For that reason, he said, keeping a blockade in reserve is a prudent U.S. course.

The most current intelligence monitoring of the Persian Gulf shows that the number of Iraqi troops inside Kuwait, together with those encamped across the border in Iraq, now totals 200,000 to 250,000, officials said. The troops are constructing defensive earth barricades at positions in the desert southwest of Kuwait City and around the international airport, which remains closed, they said.

Williams said the Iraqis were building sand barriers around their tanks and other officials said additional anti-aircraft weapons have been erected in a style that suggests Iraqi forces expect a combined U.S. Air Force and Marine assault.

Williams denied reports that U.S. Marines had already landed in Saudi Arabia yesterday. Other Pentagon officials said some Marine units are still being mobilized in the United States and others are on transport ships that just left the East Coast this week and are weeks away from arriving in the Middle East region.

Intelligence reports said that in the past two days the Iraqis also added to the defenses that already surround most of the critical military and industrial sites within their own country, including airfields, chemical weapons storage facilities and the capital city of Baghdad.

In northern Iraq near the Turkish border, the Iraqi army is also increasing the number of fortifications and state of alert of its troops, according to U.S. intelligence reports.

The initial wave of U.S. troops and warplanes arrived in Saudi Arabia yesterday, including the division ready brigade of the 82nd Airborne Division, two squadrons totaling 48 Air Force F-15 fighter planes, and five airborne warning and control planes, according to Williams.

Military officials said the pace of the U.S. deployment was being partially controlled by the need to first get equipment, supplies and weapons in place to "marry up" with the troops as they arrive.

The Air Force also began calling up unspecified numbers of reserve pilots and support forces to provide air support and communications for the troops in Saudi Arabia. The service so far is using only reservists who volunteer for active duty, according to Pentagon officials. The air guard and reserves constitute 92 percent of the Air Force's fighter-interceptor force and is responsible for about 30 percent of its aerial refueling operations. At least one F-16 attack squadron reportedly has been alerted.

Associated Press reported last night that the Pentagon's long-range plans call for sending up to 250,000 ground troops to defend Saudi Arabia, but Pentagon and White House officials said the figure was highly speculative and did not relate to the current planning for deployments to deter an Iraqi attack.

Williams said more troops and equipment will be dispatched to the region over the next several weeks, and other movements were under way yesterday that officials at the Pentagon declined to discuss.

But there were signs of them elsewhere. Overflights of U.S. transports have been sighted in Egypt and elsewhere in the Middle East, and yesterday eyewitnesses reported a line-up of 17 Air Force refueling tankers on the runways at an air base in the Azores.

Also last night, in another sign of the seriousness of the commitment to defend the Persian Gulf states from attack, the Navy prepared to deploy its two large hospital ships, USS Comfort, based in Baltimore, and USS Mercy, in Long Beach, Calif. Each is equiped with 12 operating rooms, 1,000 beds and decontamination facilities for chemical warfare.

The U.S. Customs Service yesterday also blocked the shipment from the Port of Baltimore of more than 200 containers of spare parts for U.S.-made F-18 intercepters sold to the Kuwaiti government that was ousted by Iraq's invasion a week ago.

Staff writers Ann Devroy and George C. Wilson contributed to this report.