At least three theories competed yesterday to explain Iraq's apparent decision to flood millions of barrels of crude oil into the northern Persian Gulf.

One theory, noting the battle-proven effectiveness of Iraqi combat engineers, suggested an essentially military purpose: creation of a defensive barrier against an amphibious assault. The oil slick, officials and analysts said, could slow or divert a Marine landing, clog the inductors that draw water

into naval ships, and -- if ignited on beaches or open water -- pose a potentially deadly threat to attacking allied forces.

The second theory, espoused publicly by the Bush administration, described the sabotage of Kuwait's Sea Island terminal as an act of "environmental terrorism" that, among other effects, fouls Saudi Arabian desalination plants that produce drinking water from the gulf. Iraqi President Saddam Hussein, some analysts said, might hope to dispirit public opinion with his ruthlessness or outrage American planners into an early ground assault.

The third theory, ascribing no grand strategy to the oil spill, said it was another in a series of tactical probes that sought to test allied forces and possibly disrupt them.

President Bush's angry insistence that oil sabotage would bring "no military advantage to him {Saddam} whatsoever" sparked disagreement in the Pentagon and among some outside analysts.

Dilip Hiro, whose book on the Iran-Iraq war described how Baghdad's forces dug a defensive lake east of Basra by moving 400 million cubic meters of heavy clay, described yesterday's move as a logical application of Iraqi engineering skills.

No army in history, the author asserted, has had so rich an oil resource that could be used in fabricating a defense.

"Nobody has thought of using it as a military weapon," he said. "I think this may be simply an experiment, a kind of dry run." Hiro predicted that Saddam would try to ignite the oil.

U.S. officials, including Adm. William Kime, the commandant of the U.S. Coast Guard, have said that it is difficult to burn crude oil floating on water.

"I wish they would tell us how to do it," Kime said in an interview several hours before the war began last week. "We sure could have used it in Alaska" during the cleanup of the Exxon Valdez. Some officials suggested, however, that Iraq might set the oil alight by adding gasoline to the mix.

Even unignited, officials said the oil could serve as a useful defensive barrier.

All navy vessels draw large quantities of sea water to desalinate, for drinking and on many ships to drive steam turbine engines. Though all U.S. ships draw from beneath their hulls, and even the smallest guided missile frigates has a 20-foot draft, Marine and Navy officials said a moving ship tends to draw surface water beneath it.

Marine amphibious tractors, known as Amtracks, might be capable of traversing an oil slick, one Marine official said, "but I wouldn't want to be driving through it if the enemy had the capability of setting fire to it."

An amphibious assault might strike farther north -- two-thirds of Kuwait's coastline is unaffected by the spill -- or rely more heavily on helicopters, but in either case, the oil spill would work to Iraq's advantage.

Rep. Les Aspin (D-Wis.), chairman of the House Armed Services Committee, likened the oil sabotage to Scud attacks and mistreatment of allied prisoners of war.

"What I'm guessing is he's trying to figure out some way to lure us into a ground war," he said. "If he keeps piling up outrage after outrage, he's trying to provoke people into going early."

A Pentagon strategist, saying a better comparison was with Thursday's unsuccessful incursion into Saudi Arabian waters by three Iraqi F-1 Mirages, said Saddam sought "to employ selected means to probe us, to see where we might have a weakness," without using costly resources.

Saddam lost the economic value of Kuwaiti oil to the U.N. embargo, the official said, and had no inhibitions about testing its value as a weapon.