Even with the advantages of tactical surprise, good weather and weak resistance from Iraq, U.S. airstrikes this week have destroyed or severely damaged only a small number of the first 89 targets hit, Pentagon officials reported yesterday.

The officials cautioned that the damage assessments were preliminary and based on fragmentary information, saying it will take days to get a more comprehensive picture. But with U.S. forces having nearly finished attacking all the sites on their planned target list, senior administration officials were facing a decision this weekend on whether to halt the strikes before having a complete view of the effects.

"We are getting close to hitting all the targets that we wanted to hit," said a senior military officer involved in the operation. "Now it's a matter of measuring the effectiveness of the strikes and seeing whether that was good enough.

"Within each target complex are many � sometimes dozens � of separate potential aim points. So we could continue to go back and improve on what we've done, and do that for a good long time," the officer added.

While acknowledging that some of the airstrikes have been disappointing, top Pentagon officials expressed satisfaction with the overall results, saying the attacks were achieving the main objective of diminishing Iraq's ability to make weapons and threaten its neighbors.

"We continue to be satisfied by the results, although the strikes are not yet complete," Defense Secretary William S. Cohen said at a Pentagon news conference.

In their most extensive briefing so far about the kinds of targets being pursued, senior Pentagon officials outlined an attack plan that ostensibly was focused on elements with some connection to Iraqi efforts to develop nuclear, chemical and biological weapons but also reflected larger designs to weaken Iraqi President Saddam Hussein.

While limited largely to military sites, the target list has included the country's third-largest oil refinery in Basra, justified by Cohen yesterday as a target on grounds of thwarting Saddam Hussein's illegal oil smuggling. Also blasted were television and radio transmitters, which Cohen linked to the Iraqi leader's efforts to spread propaganda to his people and jam Western broadcasts into the country.

Defense officials made clear as well that U.S. troops were aggressively targeting those Iraqi military and security forces most closely affiliated with Saddam Hussein, including his Special Republican Guard and Special Security Organization. U.S. bombs and missiles have slammed into not only the headquarters of these groups but also into some barracks in Baghdad and Tikrit, Saddam Hussein's home town, indicating a conscious U.S. effort to kill those troops on which the Iraqi leader relies to sustain his power.

Flying for the first time in combat, Air Force B-1 bombers were used during the second night of raids to drop tons of bombs on Republican Guard barracks outside Baghdad, military officials said. While the pummeling of the Guard units was officially justified under the declared objective of weakening Iraq's ability to project force, other senior military officers indicated that the Guard has been targeted as part of a larger, unspoken goal to erode Saddam Hussein's hold on power. Pentagon spokesmen said no U.S. estimates of the number of Iraqi casualties were available.

Defense officials reiterated that the targeting list had been drawn with special care to minimize civilian casualties, particularly by avoiding those commercial and industrial facilities � breweries, pharmaceutical plants, dairies � that might be converted into the illicit production of germ warfare agents.

As the bombing entered its third day yesterday, Iraq and other Muslim nations declared the start of the holy month of Ramadan, placing added pressure on the United States to stop the assault. President Clinton and other top administration officials have expressed sensitivity to carrying the airstrikes into the religious period. But they also have avoided setting any firm deadlines and indicated a strong interest in completing the intended target list, saying at the outset this could require three to five days.

Once the bombing stops, a senior defense official said the United States "reserves the right" to go back in a matter of days or weeks and strike again if intelligence indicates that some key targets remain intact.

At the Pentagon briefing, Vice Adm. Scott A. Fry, the Joint Staff's director of operations, expressed surprise at the relatively little resistance that U.S. forces attacking Iraq had encountered. While there has been heavy anti-aircraft fire from the ground, defense officials say it has been largely ineffective. And Iraq has yet to fire any surface-to-air missiles at U.S. aircraft.

"I think that they're essentially trying to protect themselves right now, and believe that that's a better tactic than trying to go and fight against the attack," said Rear Adm. Thomas Wilson, the Joint Staff's senior intelligence officer.

The Joint Staff officers showed aircraft camera tapes of laser-guided bombs slamming into an array of targets, including an early-warning radar station, a missile storage facility and a missile production plant. The brief images conveyed the impression of U.S. weapons streaking flawlessly toward their assigned targets.

But the officers also displayed several charts summarizing preliminary bomb damage assessments that indicated only a handful of targets had been judged destroyed.

For example, of five airfields struck, one emerged with "no damage." Of 27 Iraqi surface-to-air missile facilities targeted, only one was reported "destroyed" and two "severely damaged"; two had light or moderate damage; eight suffered no damage; and 14 were listed as still being assessed.

Of 11 facilities hit under the category of "weapons of mass destruction industry and production" � mostly short-range missile plants that could be used to build longer-range delivery systems � the Pentagon list showed none destroyed or severely damaged, three with moderate or light damage and eight still being assessed.

The initial reports showed U.S. forces fared better against 14 command and control facilities they struck and for which an assessment was available. Ten of the targets were said to have been either destroyed or severely damaged, among them the television and radio transmitters.

Two senior military commanders involved in the attack operation, speaking on condition of anonymity, said the early and necessarily incomplete assessments gave a somewhat distorted view of the airstrikes. They said such assessments by nature tend to be overly conservative and can easily mask the real effectiveness of a hit.

"There's a very high bar set for destroyed or severely damaged," said one of the commanders.

For example, a radar station showing only a few holes from a blast may be rated as lightly damaged, but those holes could have been enough to knock it out of commission. An airfield may be listed as undamaged entirely, when the objective was never to bomb the runway or some facilities but hit helicopters that may have been spirited away before the attack.

Defense officials acknowledged that U.S. and British warplanes have encountered particular difficulty locating and eliminating many of Iraq's mobile surface-to-air missile batteries. Even so, Fry told reporters that the air defense network in southern Iraq had been sufficiently damaged to "have created the access for pilots flying to the north."

"We in fact have had some very good success with our strikes, but not all of them have gone exactly as planned," said Gen. Henry H. Shelton, chairman of the Joint Chiefs of Staff, who also participated in the news conference.