The Iraqi troops that seized control of Kuwait last week also captured sophisticated Western military equipment from the Kuwaiti forces they swiftly overran, U.S. military officials and intelligence sources said yesterday.

A substantial portion of Kuwait's modest weapons arsenal, including several fully equipped, modern naval vessels purchased from West Germany and large numbers of artillery pieces and missiles obtained from the United States and France, was evidently captured during the Iraqi invasion, the sources said.

U.S. military specialists said yesterday that they had not determined the immediate military consequences of the seizure, but acknowledged that the arms could eventually be used by Iraq in fighting to maintain control of Kuwaiti territory and would have to be taken into consideration in planning for any attack on Iraqi forces.

"These weapons are quite capable of being used against U.S. forces, providing Iraqi military personnel are capable of operating them soon. We simply don't the answer to that right now," one official said.

Within the past several days, the Bush administration has asked the Soviet Union, Iraq's principal arms supplier, for detailed information on Iraqi weaponry and military proficiency, another official said, but Moscow has not decided whether to provide it.

The Kuwaiti naval force of eight guided missile patrol boats captured by Iraq could pose a threat to U.S. and allied naval forces assembling near the Persian Gulf in preparation for a potential blockade of Kuwaiti and Iraqi ports, one official said. Each vessel is believed to be equipped with sophisticated French-made Exocet antiship missiles, and two are capable of laying mines.

The official cautioned, however, that Iraq has less sophisticated ships in its navy and may experience difficulty operating the guided missile boats.

The Iraqis also are believed to have taken control of antiaircraft batteries around Kuwait City, including some armed with U.S.-made Hawk missiles. A substantial portion of the Kuwaiti arsenal of several thousand U.S.-made TOW antitank missiles has also fallen in Iraqi hands, officials said. The weapons are not the latest versions available to U.S. forces, however.

"There is nothing in Kuwait's arsenal of U.S.-made weapons that will change the balance of power," said Leland Ness, a military market analyst at the Teal Group in Washington.

Several U.S. officials said the military threat posed by the invasion could have been far worse if Iraq had gained control of advanced U.S. F/A-18 fighter aircraft and associated weapons, including sophisticated antiship and antiaircraft missiles, that were sold to Kuwait in 1988 but are not slated for delivery until 1992.

Before the contract was signed, Kuwaiti officials said they wanted the planes partly to defend against any future Iraqi military threat. But several congressional aides said the swift surrender of most of Kuwait's military forces undermined the sincerity of that claim.

U.S. officials said they are also relieved that virtually all Kuwaiti fighter aircraft, including two squadrons of French-built Mirage F-1s and several dozen older U.S.-made A-4 Skyhawk aircraft, escaped capture because they were evacuated to air bases in Saudi Arabia before Iraqi troops crushed Kuwaiti infantry and security forces near the capital.

Intelligence sources estimate that as many as 400 to 600 Kuwaiti soldiers and several hundred Iraqi soldiers perished in the skirmishes. Portions of several large Kuwaiti army units escaped into Saudi territory with their equipment, including some tanks and armored vehicles.