Fewer than half the Argentine bombs that hit British ships off the Falkland Islands actually exploded, perhaps enabling Britain to win a war it otherwise might have lost, a Pentagon official said on the basis of top-secret, after-action reports.

At least six British ships were discovered to have unexploded Argentine bombs lodged deep inside them, he disclosed earlier this week.

A high-level British commander has told the Pentagon that he would have recommended withdrawing the fleet from the Falklands rather than accept the losses projected if all the Argentine bombs put on target had exploded, the defense official said.

Most of the bombs used against the British fleet were bought from the United States about 13 years ago, an Argentine officer said yesterday, and some of their circuits may have deteriorated.

But the most likely reason for the failures was that the Argentines were trying to sink ships with bombs rigged to destroy land targets, U.S. and Argentine officials agreed.

The more modern French Exocet antiship missile had its failings, too, the Pentagon executive said. He confirmed that the Exocet that sunk the British destroyer Sheffield carried a bomb that failed to detonate. The Sheffield was sunk by explosions touched off by the missile's burning fuel, he said.

In yet another bad break for the Argentine military, its only aircraft carrier, the 25th of May, had a mechanical breakdown at the outset of the war and was kept home because of the threat of British submarines, the Pentagon official said.

An Argentine military official corroborated the defense official's revelation that bomb after bomb failed to go off after landing smack on a British ship.

The Pentagon official warned against assuming that the same thing could not happen to the U.S. military, revealing that up to 70 percent of more modern Navy bombs have failed to explode in some situations. He did not elaborate, but Navy sources said the failure rate has indeed been as high as 70 percent in recent ocean exercises with bombs detonated by electrical signals.

The Argentine official said his country had mostly 500- and 1,000-pound American-made bombs designed to destroy land targets, not ships. The pilot had no way to control their detonation once he released them, the Argentine said.

Instead, propellers on the bombs had to spin a certain number of revolutions before the bombs could explode, he said. Argentine pilots often flew so low over the sea to escape British radar and anti-aircraft fire that their bombs did not have time to become live during the short flight from plane to ship.

Another failing, he said, was that many of the bombs had fuses to delay their detonation for several seconds after impact. This was to enable the bombs to penetrate into the vulnerable innards of the ship, like ammunition storage areas, and also to give the plane time to escape the blast.

A third problem, he said, was that some of the bombs were set to explode only after absorbing more impact than that provided by the thin sides of some British ships. "It's hard to believe," the Argentine officer said, but in several instances a bomb entered one side of a British ship and came out the other without exploding. "Some of the ships were like butter," he said.

If all the bombs that hit British ships had exploded, said the Pentagon official, the war's outcome "might have been different." He discussed the after-action reports piling up in the Pentagon on a background basis, meaning that what he said could be reported but not attributed to him by name.

The disclosures about Argentine bombs turning out to be duds reminded Navy historians of the disastrous record of U.S. torpedoes early in World War II. Like the Argentine bombs, many of of those torpedoes clanged into the side of enemy ships but did not explode. Some torpedoes turned around and pursued the submarines that launched them, they said.

Argentine pilots paid an enormous price for braving British fire in attacking ships off the Falklands, according to the Pentagon official. More than half the attacking planes were lost, he said.

In the only dispute with the Pentagon account, the Argentine official said his country's casualties on the 505 sorties flown were "high . . . but not 50 percent." He said the number "is confidential."

The Pentagon official said the British sorely missed the long reach of carrier-based attack planes such as the F14 to protect their ships. Instead, they had to rely on Harrier jump jets, which, according to the Pentagon executive, "failed to keep the enemy off the ships and off the beaches." He said "one-third" of the Harriers sent to the Falklands were lost.

He also said that after-action reports indicate a British sub sunk the Argentine cruiser General Belgrano with 50-year-old torpedoes rather than the highly touted and modern Tigerfish that were credited in many accounts at the time.