DHAHRAN, Saudi Arabia (AP) _ The British said Sunday the Royal Air Force apparently knocked out a Silkworm missile site in Iraq. The U.S.-led allied forces moved to stop a colossal oil slick, and military officials said the spill would not interfere with the Persian Gulf war.

At a briefing in Riyadh, the Saudi capital, Royal Air Force Group Capt. Niall Irving said one RAF plane ''scored a direct hit on a Silkworm missile site'' in Iraq. He said the Chinese missile could have posed a threat to allied navy or merchant ships.

Irving said British planes also struck an ammunition storage site in western Iraq on Saturday. He said there were ''incredible secondary explosions'' after the initial bombing by RAF aircraft.

In Washington, Defense Secretary Dick Cheney said Sunday the United States has taken military action to try to halt the oil spill. But he did not elaborate, saying, ''I don't have the results yet.''

Along the northern front lines of the war, Iraqi forces and troops of the U.S.-led coalition exchanged fire.

Marines unloaded their heaviest barrage yet on forward Iraqi positions, with 155mm howitzers, and the Iraqis fired short-range missiles that fell harmlessly in the desert, allied officers reported.

Iraq fired another round of Scud missiles at Saudi Arabia and Israel, but all were shot down by U.S. Patriot missiles, allied officers said.

But it looked increasingly like a ground offensive to drive Iraq from Kuwait will be on hold until well into February. American armored forces are at least two weeks from full strength, military officials said.

Baghdad hinted late Saturday in a broadcast on Iraq's new ''Mother of Battles'' radio that it would use unconventional weapons against the allies.

Allied fighter pilots, meanwhile, continued their furious bombing of Iraqi positions in Kuwait and southern Iraq, which they described as a devastated landscape of shattered bridges and fires beyond number.

The U.S. command also said Air Force F-15s had shot down three Iraqi MiG- 23s over Iraq, according to a preliminary report.

The Pentagon also said 24 Iraqi planes recently flew to neighboring Iran, apparently fleeing an American air attack or Saddam Hussein's government. Tehran said it would keep the planes grounded until the war ended.

The gigantic oil spill at the head of the Persian Gulf was reported Saturday to be 30 miles long and eight miles wide.

Abdulbar al-Gain, a Saudi environmental official, said Sunday that the slick does not threaten Saudi Arabia's water supply because the kingdom's desalination plants are being protected. He said, however, that the slick was endangering marine life and birds.

A Saudi Aramco oil executive, meanwhile, said Sunday that the oil that has already fouled Saudi beaches and killed seabirds was probably not from the spill caused by the Iraqis but from a ruptured tank in Khafji, about 10 miles south of the Kuwaiti border. Abdulaziz M. al-Hokail acknowledged, however, that there were indications the oil might actually have come from Kuwait, where there have been repeated allied air strikes on Iraqi positions.

He said the oil from the main spill was still two to three miles off the coast of Saudi Arabia on Sunday morning. Television footage showing oil birds and beaches was shown on television Saturday.

The allies said the Iraqis opened valves Tuesday at the main Kuwaiti supertanker loading station, 10 miles offshore from the Al-Ahmadi refinery complex, and also fed the large spill from five loaded tanker ships.

The U.S. military said the tankers held about 125 million gallons, and speci 0 l, from a military standpoint, the oil slick is minimal,'' said Lt. Col. Mike Scott of the U.S. Air Force. ''But from an environmental standpoint, you can see it is going to have a major impact.''

Drifting oil could present some difficulties for an allied amphibious landing in Kuwait. Oil also was devastating the northern gulf's environment.

Cormorants and other seabirds coated with oil were dying on Saudi beaches. Environmentalists expressed fears for the dolphins, turtles and other marine life that thrive in the gulf's warm waters.

At Jubail, 160 miles south of the terminal, oil booms were being floated into position to protect a large plant that converts saltwater to drinking water for Riyadh and for hundreds of thousands of allied troops.

The ''Mother of Battles'' radio said ''the power that the Iraqis have mustered to confront the U.S. and Zionist (Israeli) aggressors is not a conventional one.''

''All the potential, resources and capabilities are in our favor,'' said the radio, monitored in Nicosia.

Iraq did not specify what it meant by non-conventional, but Saddam Hussein is known to have an arsenal of chemical and biological weapons.

Clear skies apparently enabled Desert Storm pilots to mount a full day of bombing strikes, zeroing in on military-support targets in southern Iraq and Kuwait.

Returning pilots reported knocking out an airfield and hitting two railroad bridges in southern Iraq, said Air Force Lt. Col. Mike Scott, a U.S. command spokesman.

He said one F-4G Wild Weasel pilot reported back: ''There are more fires down there than I can count.'' The fires may have been both allied hits and oil fires set deliberately by the Iraqis.

Bombers continued hammering away at the dug-in positions in southern Iraq of the Republican Guards, the elite core of the Iraqi defense in Kuwait.

A Baghdad military communique claimed air defenders shot down three more allied warplanes or missiles, bringing Iraq's total claimed ''kills'' to 180. The allies have reported the loss of only 17 planes in combat, including 10 American.

On the front lines, the Marine 155mm batteries opened fire on Iraqi positions midway along the Saudi-Kuwaiti border, 1st Marine Division officers reported. Twice before, Marine gunners had moved up to the border, fired off rounds and then pulled back, but this was the biggest barrage yet, they said.

Back behind the lines, it appeared the allied buildup was going slowly.

''I feel no pressure to do it tomorrow,'' Col. Bill Nash, commander of the 3rd Armored Division's 1st Brigade, said of the expected allied ground offensive.

Iraq invaded Kuwait on Aug. 2 in a dispute over land, oil and money. President Bush, saying he doubted trade sanctions would force Iraq out, began the Desert Storm offensive Jan. 17, one day after the expiration of a U.N. Security Council deadline for Iraq to withdraw from the occupied emirate.