U.S. B-52 bombing of Iraq's elite Republican Guard forces, underway for at least two days, has only begun to accomplish the damage desired by military commanders, U.S. officials said yesterday.

An estimated four dozen of the massive, high-flying bombers have been hitting Republican Guard enclaves in northern Kuwait and southern Iraq with tons of high explosive, anti-armor and anti-personnel weapons, the sources said.

Officials said the B-52s flying from Diego Garcia, an island in the Indian Ocean roughly 3,400 miles from Iraq, and from Jiddah, Saudi Arabia, are the largest and most destructive aircraft in the Persian Gulf War. Besides hitting the Republican Guard, since the war began they have assaulted Iraqi airfields, railroad tracks and oil storage sites.

But preliminary damage reports indicate that many more B-52 raids will be needed before the Guard's military capabilities has been significantly diminished, and some experts who favor using ground forces in the war question whether the bombers will ever be successful.

One knowledgeable source calibrated the level of damage to the Guard at only 5 to 10 percent of "what we want to do," and a second official said he concurred. "The B-52 will come into its own . . . when we turn our attention in a serious way to the Republican Guard," a Pentagon official said yesterday. "We have yet to really concentrate on that as a target set."

U.S. officials said that the B-52s have so far conducted fewer than 200 "carpet-bombing" raids in which more than 100 bombs are released simultaneously by several aircraft to wreak widespread destruction beneath their flight path.

Although the operation benefits from modern, computer technology -- in the plane and the weapons -- its character is essentially the same as in the strategic bombing of Vietnam from 1965 until the early 1970s. The aim then and now is to vanquish concentrated military forces and to demoralize individual soldiers.

"Of all the Air Force weapons employed during the war in Southeast Asia, none had a more devastating effect on the enemy than the B-52 Stratofortress," said Air Force historian Carl Berger in a 1984 book on the air war against Vietnam. The Air Force's favorable viewpoint was not altered by criticism during the war that it was using a "sledgehammer" to "swat flies" on the ground.

The B-52 "G" models flying over targets in Kuwait and southern Iraq use sophisticated equipment to increase accuracy of unguided bombs that weigh between 250 and 2,000 pounds each. The timing of their release is determined by computer-assisted calculations of aircraft altitude, speed, force and direction of wind and atmospheric pressure, among other factors.

Unlike some ground-attack aircraft, the B-52s fly at high altitudes and have radars powerful enough to allow their use in virtually any weather.

In addition to dropping World War II-style concussion bombs packed with high explosive, the B-52s in the Persian Gulf have released a variety of anti-personnel and anti-armor canisters, which fire off like grapeshot to cover an area the size of a football field with hundreds of small bombs designed to penetrate tanks, destroy radars and inflict heavy casualties.

An Air Force official said the "weapon of choice" among B-52 crews is the CBU-87 Combined Effects Munition, which dispenses 202 "bomblets" in a pattern tailored to specific targets and includes both steel fragmentation and incendiary explosives.

"Dropping large clusters of bombs is the safest and most effective way to go after the Republican Guard forces," one official said. "You don't have to take them out tank by tank."

Lt. Gen. Thomas Kelly, operations director for the Joint Chiefs of Staff, told reporters yesterday that although logistical support facilities for the Republican Guard appear to have been damaged, "I can't quantify it." He said that foul weather in southern Iraq and northern Kuwait have recently obstructed a detailed damage assessment.

Iraqi President Saddam Hussein is estimated to have deployed nearly 110,000 Guard troops in that area as potential reinforcements in an eventual ground war if U.S. and allied forces move north of the Saudi-Kuwait border. During the past five months, the troops have amassed protective armor and erected camouflaged concrete bunkers and other fortifications to resist the aerial bombardment.

A Defense Department tally yesterday of Iraqi forces in the theater included the same number of troops, tanks and infantry fighting vehicles listed before the war began, indicating that confirmed attrition of forces from bombing has not been significant.

The Air Force flew roughly two dozen of its 134 B-52G aircraft to Diego Garcia months before the war began, then moved the planes to Jiddah after Jan. 16 and sent another contingent of about the same size to Diego Garcia, several officials said. The slowly manuevering aircraft have avoided flying over heavily defended targets near Baghdad and elsewhere to avoid being shot down.