U.S. warplanes blew up two Kuwaiti petroleum pipeline complexes to prevent Iraq from adding to the several million barrels of crude oil already dumped into the Persian Gulf, the Operation Desert Storm commander said yesterday.

F-111 fighter-bombers fired television-guided "smart" bombs at the coastal manifold facilities in an effort to sever the pipeline between inland oil fields and an offshore supertanker terminal where crude had been gushing into the gulf since Jan. 19, Gen. H. Norman Schwarzkopf announced in Riyadh, Saudi Arabia.

"I think that we've been successful, but only time is going to tell," Schwarzkopf said. Despite his cautious optimism yesterday, the commander conceded it is "entirely conceivable" that Iraqi President Saddam Hussein could order the sabotage of another Kuwaiti oil terminal.

Schwarzkopf said he learned of the spill early on Friday and immediately conferred with military, environmental and engineering experts to come up with a limited counterstroke that would avoid "destroying Kuwait while we are liberating Kuwait."

As those experts suggested, the fountainhead of oil pouring into the gulf was set afire Friday night, albeit inadvertently during a U.S. Navy skirmish with an Iraqi patrol boat discovered near the Sea Island Terminal eight miles from the Kuwaiti coast. The fire, experts told Schwarzkopf, will incinerate some of the spill's pollutants.

Then, at 10:30 p.m. Saturday (2:30 p.m. EST) the F-111s struck the two manifolds, a critical complex of pipes and valves located five miles inland to control the river of crude sweeping from the oil field to the supertanker loading terminal through huge underwater pipes.

Displaying videotapes of the burning oil taken before and after the F-111 attack, Schwarzkopf said the more recent pictures indicated that the flow of crude has diminished significantly. The commander also showed dramatic videotapes taken through the nose of the GBU-15 bombs as they raced toward the manifolds before detonating.

In summarizing the weekend war news, Schwarzkopf also announced that two U.S. F-15 Eagles destroyed four Iraqi MiG-23s in a dogfight just southeast of Baghdad at 11:20 a.m. yesterday (3:20 a.m. EST). Those kills brought to 26 the number of Iraqi jets shot down in air-to-air combat, the commander said, compared to zero allied losses reported.

Iraqi aircraft, including some of their best fighters, continued to flee into neutral Iran. Twenty-three jets -- nearly the equivalent of a squadron -- landed in Iran during a 24-hour period ending at 7 p.m. Saudi time yesterday, Schwarzkopf said, bringing to at least 39 the number of such aircraft detected by allied intelligence since the war began Jan. 17.

Whether the pilots are defecting, attempting to provoke an allied attack on Iranian airfields or looking for a safe haven from which to fight back remains uncertain, U.S. officials said. Iran declared this weekend that any plane landing on its territory will remain there for the duration of the war. Schwarzkopf said "we should take Iran at its word," although the allies will carefully watch for signs that those planes are reentering the fray.

During its eight-year war with Iran, Iraq occasionally flushed its threatened warplanes to other countries -- reportedly including Saudi Arabia -- so they could live to fight another day. Although allied fighters are believed to be watching for fleeing planes, the Iran-Iraq border is more than 700 miles long and impossible to seal completely, U.S. Air Force officers have said.

Other than sporadic artillery and rocket duels, the ground war remained quiescent yesterday. Allied naval forces continued to hunt Iraqi patrol and mine-laying boats in the northern gulf and near Bubiyan Island, and have sunk or badly damaged 18 such vessels to date, Schwarzkopf said.

The second Sunday of the war found much of the nation enjoying an uneasy day of rest, culminating in last night's Super Bowl. At Tampa Stadium in Florida, more than 2,700 security guards, undercover police and federal agents mingled with 72,000 football fans to forestall any violent protests or terrorist attempts. Security measures usually reserved for airline passengers -- including X-ray machines and metal detectors -- were used to screen those entering the stadium, which lies 10 miles from MacDill Air Force Base, peacetime headquarters for Schwarzkopf's Central Command. Although kickoff came at 2 a.m. Saudi time, thousands of U.S. troops stayed up to follow the 25th annual championship game.

In the desert kingdom, however, the Super Bowl was overshadowed by news of the oil spill, which Pentagon officials have said could be a dozen times larger than Alaska's Exxon Valdez disaster in 1989. Saudi officials yesterday said the slick probably will not threaten the kingdom's water supply but does pose a major threat to seabirds and other Persian Gulf wildlife. Desalination facilities are protected with booms, crude oil skimmers and unspecified "non-traditional" methods, environmentalist Abdullah Ghain said.

The bulk of the spill, which extends southward to Ras Mishab in a ragged oblong of 6 million to 10 million barrels, 35 miles long by 10 miles wide, is still two to three miles off the Saudi coast, according to a Saudi oil executive. Iraqi Claims Rejected

In reconstructing the oil spill and allied efforts to combat it, Schwarzkopf adamantly denied Iraqi claims that U.S. military strikes had caused the disaster. To bolster his denial, the general noted that five tankers -- said by the Pentagon to contain a total of 3 million barrels of oil -- had been berthed in Kuwait on Jan. 16, "low in the water . . . completely full of oil." Eight days later, Schwarzkopf said, the ships "were riding very, very high in the water," apparently because Iraqi forces had pumped their cargo into the gulf.

In applying a kind of combat tourniquet to the crude gushing from inland storage tanks, Schwarzkopf said he "certainly didn't want to go in and completely destroy the oil field." Setting the Sea Island Terminal ablaze was intended to incinerate as much of the polluting oil as possible. Attacking the two manifolds, which lie 3 1/2 miles apart, was seen as an effective means of stanching the flow but with damage that can be repaired in two weeks once Kuwait is recaptured, Schwarzkopf said.

The attacking bombers, delayed until Saturday night by bad weather, encountered no Iraqi antiaircraft resistance, the commander said. Noting that yesterday's photographs of the terminal showed that oil is still burning, although less furiously than the fireball conflagration of the previous day, Schwarzkopf suggested that the blaze was still being fed by 13 miles of oil still in the pipeline from the manifold. "It will take more than 24 hours before the fire goes out," he added.

Schwarzkopf reiterated U.S. government assertions that the spill, while ecologically calamitous, will have no significant military impact and will not affect the allied war timetable. Noting that "war is not a clean business," the general recalled as a boy in New Jersey seeing "dirty oil balls" washing ashore from ships torpedoed by German U-boats in World War II.

Asked whether considerations of an ecological catastrophe should be a factor in deciding whether to wage war against Saddam, Schwarzkopf -- describing himself as "a lover of the environment {and} a conservationist" -- said he believed that to be "a ridiculous argument" outweighed by the need to stop the "despot" Saddam.

President Bush returned to the White House yesterday afternoon from Camp David, offering no comments to reporters as he entered the White House. As a security precaution, the presidential helicopter was accompanied by several decoys on the short flight from the Maryland mountains. Although the precaution is commonplace, yesterday more decoys than usual seemed to be in the formation and they swooped past the Washington Monument toward the South Lawn before pulling away.

Bush also called British Prime Minister John Major for a brief conversation about the war, White House officials said. In a briefing in Riyadh, a Saudi commander said Royal Air Force Jaguar bombers "scored a direct hit" on an Iraqi Silkworm missile site that posed a threat to allied navy or merchant ships in the Persian Gulf. Group Capt. Niall Irving said Jaguars also struck an ammunition dump over the weekend, triggering "incredible secondary explosions."

Eight other British planes conducted two sweeps over a radar site, the group captain added, also noting that a "major communications site . . . no longer exists."

"We are gradually winning," Irving said of the allied effort, "but we're doing it in a phased way."

Iraq yesterday blamed U.N. Secretary General Javier Perez de Cuellar for the "ugly crimes" of allied forces, including alleged attacks on civilian, economic and religious targets. A spokesman for the United Nations, which last year passed a dozen resolutions condemning Iraq and eventually authorizing the war, said Perez de Cuellar would have no comment yet on the charge, delivered in a letter from Baghdad and also aired on Iraq's new "Mother of Battles" radio.

A military communique broadcast on Baghdad Radio promised to turn the "monstrous entity" Israel into "a dead leaf discarded on the ground." Iraq has "not started its crushing strikes which will burn {allied} troops and their black intentions," the communique declared in a possible reference to Iraq's hidden stocks of chemical weapons. Border Post Reopened

Iraq yesterday reopened its border with Jordan for the first time in four days, permitting a trickle of refugees to leave the country. Only 70 Tunisians and one Jordanian family crossed the border by midafternoon, although witnesses estimated that 3,000 to 5,000 people had gathered at the snow-covered Iraqi border post of Trebil.

Some travelers said Iraq had ordered thousands of the cold, hungry refugees to return to Baghdad for exit visas. But because Iraq has stopped selling fuel at gasoline stations, witnesses added, few of the stranded families can get back to the Iraqi capital even if they wanted to run the gantlet of allied bombing during the 10-hour journey.

Red Cross officials trucked some food into Trebil yesterday. And on Iraq's eastern frontier Iran is sending emergency supplies of bread, dates, powdered milk and biscuits, the Iranian news agency IRNA reported. The Iranian gesture is to help ease "the difficult conditions caused by food and medicine shortages" in Iraq, the IRNA report said, and is consistent with U.N. Security Council directives allowing certain humanitarian supplies to slip through the worldwide trade embargo against Iraq.

As allied bombers swept across Iraq and Kuwait -- bringing to more than 22,000 the number of sorties flown in the war since Jan. 17 -- Defense Secretary Richard B. Cheney said the administration has always assumed a ground attack would be necessary to reclaim Kuwait. In an appearance on NBC's "Meet the Press," Cheney predicted that allied ground forces will be ready within the next four weeks.

"The key requirement before we commit forces to a ground war is to make absolutely certain that we've gained everything we can from the air campaign," Cheney said, adding, "there's no reason for us to rush into a ground conflict which would mean unnecessary American and allied casualties."

After Patriot missiles parried a volley of Iraqi Scuds loosed against Israel and Saudi Arabia Saturday night, the missile war was quieter yesterday. Moshe Arens, the Israeli defense minister, said his country cannot retaliate for the 25 Scuds launched at Israel until developing "a level of understanding and coordination with the United States" and its military "that would prevent uncontrolled encounters between our aircraft and U.S. aircraft."

Arens and Egyptian national security adviser Osama Baz said they expect renewed efforts to resolve the various conflicts in the Middle East after the battle over Kuwait has been settled. Another Egyptian official, Boutros Ghali, said Cairo does not wish to see the Iraqi armed forces destroyed and will support the allied effort "only to obtain the liberation of Kuwait."

That battle is now expected to cost the United States about $50 billion this year, White House Chief of Staff John H. Sununu said yesterday. Contributions from other countries should cover all but $15 billion of the bill, obviating the need for a tax increase to pay for the war, Sununu said in a television interview. Budget director Richard G. Darman said the $15 billion estimate of undefrayed U.S. costs will be included in the Bush budget going to Congress shortly.

Staff writers Barton Gellman and Michael Weisskopf and staff researcher Lucy Shackelford contributed to this report.