WASHINGTON -- If Saddam Hussein used chemical and biological weapons against invading American forces, could American troops survive them?

U.S. defenses against chemical and biological attack have improved greatly since the 1991 Gulf War exposed major flaws. Detection equipment is better, and an array of preventive and post-attack medicines is available for most chemical and biological agents.

But protective clothing and shelters remain inadequate and defective, experts say.

"We can say things are better from a medical and prevention point of view, but we can't say they're good enough," said Brad Roberts, a researcher at the Institute for Defense Analyses, a military think-tank in Alexandria, Va.

The Defense Department's annual report on chemical and biological defense and a report earlier this month from the General Accounting Office, an investigative arm of Congress, spotlighted problems supplying the military with enough protective clothing and shelters.

Despite spending more than a billion dollars a year on chemical-biological preparedness, the Pentagon lacks millions of needed boots, masks, gloves and suits; provides inadequate training for chemical and biological attack; and doesn't have enough specialized medical shelters to treat the wounded on a contaminated battlefield, the analysts concluded.

"A real gap exists between the priority and emphasis given chemical and biological defense by DOD and the actual implementation of the program," Raymond Decker, GAO's director of defense capabilities, told Congress. "Risk (to troops) will be increased unless the persistent problems in the chem-bio defense area are addressed," Decker told Knight Ridder.

The Navy, for example, is short more than 1 million protective suits and boots, according to the GAO and Pentagon reports. The Air Force has fewer than half the protective suits it needs; the Marines have fewer than half of the boots required.

In addition, about 250,000 of the military's more than 4 million protective suits are defective, but the Pentagon can't identify all the ones that won't work. Isratex Inc., a now-bankrupt company whose president was jailed for deceiving the government, sold 800,000 defective chem-bio suits to the Pentagon a decade ago. The military has found and destroyed 550,000, but officials haven't been able to locate the rest.

The Pentagon may try to reduce the risk by striking faster with a smaller, more mobile invasion force, but senior military officers say they would still have to mass their troops to punch a hole in Iraq's defenses.

"And when we mass, that's when he would gas," said one officer, speaking on the condition of anonymity.

Some Pentagon officials also worry that by making it clear that their goal is "regime change," unlike in the 1991 Gulf War when the goal was to drive Iraqi troops out of Kuwait, President Bush has left Saddam with nothing to lose by trying a chemical or biological attack.

Despite the problems and the fears, George Allen, deputy director of the Defense Supply Center Philadelphia, which stocks protective gear, told Congress recently that "we could equip the force that is envisioned today with good suits, and know with virtual assurity that they are all good suits."

The GAO's Oct. 1 report, however, said the Pentagon "had inaccurately reported the risk (to troops) in most cases as 'low'."

The problem, the GAO said, is that the military based its assessments on individual pieces of protective equipment, such as gloves and boots, and ignored the fact that they must be used together, and one missing piece would make the entire suit useless.

It's not just clothing, said Pentagon Inspector General Joseph Schmitz. The military has only 5 percent of the number of chemical/biological protective shelters it needs in order to provide medical treatment on a contaminated battlefield. The Army, which may need them most, has none.

In addition, key military units have not been adequately trained to withstand chemical and biological attacks, Decker and Schmitz said in testimony.

Despite these problems, most experts in and out of government remain optimistic about the military's ability to survive chemical or biological attacks.

U.S. military forces have enough vaccines and post-attack medicines to counter most of the biological and chemical agents that Saddam is thought to have, including anthrax, botulinum toxin, smallpox and even plague, said Ronald Blanck, a former Army surgeon general. He is now president of the University of North Texas Health Science Center in Fort Worth.

This summer, the Pentagon resumed vaccinating military personnel against anthrax, and this month it is acquiring 1 million doses of smallpox vaccine.

In addition, the detectors that sniff the air and soil for chemical and biological attacks work fairly well, although they take about 40 minutes to find out if there has been an attack, said Richard Pilch, a scientist at the Center for Nonproliferation Studies in Monterey, Calif. The military would use them ahead of troops, which would give soldiers enough warning to don protective equipment.

"Do I believe everything is perfect? Of course not. But do I believe everything is better than it was? Absolutely yes," Johnson-Winegar of DOD told Congress.

In the absence of combat experience, however, no one can be certain how well U.S. protective gear might work.