U.S. and Spanish warships have seized a Soviet freighter bound for Jordan with a cargo of military spare parts, but U.S. officials were unable to say yesterday whether the Soviet vessel was trying to evade the U.N. embargo on Iraq by shipping the cargo through neighboring Jordan.

Both U.S. and Soviet officials acknowledged that the cargo ship, Dimitry Fermanov, was halted Friday by the guided-missile cruiser USS Mississippi and the Spanish frigate Infanta Cristina in the Red Sea while en route from Odessa to the Jordanian port of Aqaba. It remains surrounded by the warships and has not been allowed to proceed.

Defense Department spokesman Pete Williams said yesterday that its cargo includes command and control vehicles, rocket launchers, explosives, tank parts and communications equipment. The Soviet Foreign Ministry announced in Moscow that the materiel was intended for the Jordanian army.

However, Williams said, "There is some question in the manifest about precisely what their destination is." Jordan has some Soviet equipment in its arsenal, but most of its weapons come from the United States and Britain.

Before the United Nations imposed the embargo in retaliation for Iraq's occupation of Kuwait Aug. 2, the Soviet Union was Iraq's largest military supplier. However, Moscow has been a strong supporter of the embargo, and U.S. officials yesterday stepped gingerly around questions about the cargo.

"The situation is still not resolved, and we don't have a very clear understanding of what happened there," White House spokesman Marlin Fitzwater said.

State Department spokesman Richard Boucher added: "Whatever the ship was up to, the Soviet Union has been steadfast and consistent in its support for the U.N. resolutions and its support for the policy that the international community has taken in the {Persian} Gulf. We'll have to see exactly what the cargo is and what the explanation is. . . . "