Outfitted in full-body protective suits with air tanks, three members of the Missouri National Guard grope methodically through a mock terrorist lair looking for lethal chemicals amid scattered canisters and overturned jars.

The scene, during an exercise here last week, is set up to resemble an apartment in Washington's Anacostia neighborhood that has just been raided by the FBI on a tip that terrorists were planning a chemical or biological attack on the nation's capital. The Guardsmen, members of a new force being trained and equipped for combating unconventional weapons, have less than an hour--the time it will take for their oxygen to run out--to scour the premises and identify hazardous materials.

They move too slowly and fail to spot some dangerous items in the apartment's makeshift laboratory before withdrawing. A second team ventures in. Military specialists coaching from the sidelines attribute the first group's shortcomings to inexperience but commend the reservists for not blowing themselves up.

As concern grows that a rogue state or terrorist group might someday unleash biological or chemical agents in a U.S. city, the Pentagon is investing tens of millions of dollars to convert part of the Guard into an emergency response force. Equipped with sophisticated gear for analyzing mysterious substances, the first 10 units, each with 22 members, are scheduled to go into operation by January.

But are they really necessary? The FBI already has a hazardous materials unit ready to rush to the scene of an attack. So do the active-duty Army and Marine Corps. Many local police, fire and health agencies also are preparing for the threat of biochemical attack.

A recent report by the General Accounting Office argued that the Guard units--known as RAID teams, for Rapid Assessment and Initial Detection--are redundant and their mission poorly defined. The congressional watchdog agency also challenged the ability of the RAID units to respond quickly and effectively to an attack. It urged Congress to reassess the program and restrict funding for additional teams.

Congress so far has ignored the advice. At the urging of the Senate Armed Services Committee, which wanted to fund 17 more RAID teams, Senate and House conferees last month authorized 12 more in fiscal 2000.

Starting with $20 million appropriated last year for the first 10 teams, Congress has quickly expanded the program. It added $19 million last autumn for more equipment, plus $13 million to establish RAID "light" teams in states lacking full-fledged contingents. The latest defense authorization bill would provide an additional $64 million.

Congressional funding for the RAID initiative fits with the strong backing that lawmakers have historically afforded the Guard, which has members in almost every district. In fact, some critics regard the RAID teams largely as an effort to find a new mission for the Guard and help it avoid deeper budget cuts in the post-Cold War era.

"It's basically become an attempt to find something the Guard can do, from what we can tell," said Ann Borseth, a defense analyst who worked on the GAO report.

Senior Pentagon officials reject such criticism, vigorously defending the Guard units as essential elements in a developing national plan to provide a many-layered response--from local to federal levels--against attacks involving chemical, biological or radiological agents.

Under a separate multimillion-dollar program, local police, fire and health departments in 120 cities also are being trained to deal with what the Pentagon calls weapons of mass destruction. But defense officials say attacks of this kind, with their broad potential for casualties, would likely overwhelm local units.

The Guard teams are intended to give state governors a small expert force to help detect and identify whatever biological or chemical element may be released and coordinate the involvement of other federal troops. Their members include many former active-duty military specialists in chemical warfare. And unlike most of the Guard, which serves part-time, these units require a full-time commitment and will be on 24-hour alert.

Still, one of the chief concerns for critics is the time it will take a RAID team to reach the scene of an attack. In a chemical incident, the first hour or two is critical. But the Guard teams, which have no military aircraft dedicated to them, cannot guarantee a response time of less than four hours.

"All local, state and federal officials we met with expressed concern that this time frame would get the team there too late to be useful," the GAO report said.

In the event of a biological attack, the role of the Guard teams is even more questionable, critics say. Because germ agents such as anthrax or smallpox can be released inconspicuously, there is little likelihood of knowing an attack has occurred until hours or even days later, when sick people start showing up at hospitals or doctors' offices.

"I'm quite puzzled about what exactly the RAID teams would do in the event of a biological attack," said Donald Henderson, a professor of epidemiology at Johns Hopkins University and head of the Center for Civilian Biodefense Studies. "The job of detecting a germ agent will rest with physicians and hospital emergency room personnel, coupled with state and local health department people and their laboratories. What we really need are more epidemiologists."

The interaction of RAID teams with local authorities also is problematic. Many police, fire and health departments already have experience working with each other, as a result of coping with industrial spills and natural disasters. They have little practice dealing with the Guard.

"The problem is, it's going to be hard to integrate them into our normal emergency operating procedures," said Gary Briese, executive director of the International Association of Fire Chiefs. "We respond to emergencies daily, and if most of the time we never see the RAID teams--if they only expect to show up for one in a thousand responses--then coordinating with them isn't likely to go smoothly."

Plans call for the RAID units to start training regularly with city emergency response teams, and defense officials express confidence that the Guard squads will be able to contribute a new thing or two.

"You'd be surprised at how little capability exists in some of the larger cities of our country," said a military official supervising the Pentagon effort. "Our people have been through 700 to 1,200 hours of training each, including courses taught by about 20 different agencies, among them the National Fire Academy, the Environmental Protection Agency and the Department of Energy. There isn't a response unit in the country that comes close to that."

At the Army base here, RAID teams from around the country spent several weeks this summer practicing responses to some of the attacks they consider possible. There was the national fur convention scenario, in which animal rights activists let loose balloons loaded with botulism germs. And the gay rights parade scenario, which also involved balloon weapons, this time filled with the nerve agent ricin in powder form.

A scenario set in downtown Boston envisioned an exploding trash can releasing GF gas, a powerful nerve agent. Another story line began outside Salt Lake City's Delta Center, with a terrorist trying to pump a deadly liquid into a fire hydrant. And still another exercise imagined a Seattle office building, where a rash of illnesses among office workers led to the discovery of a terrorist group preparing a radiological dispersion device using cobalt-60.

To detect the lethal substances they might come up against, the RAID teams were given $70,000 mass spectrometers, which show a characteristic pattern of lines for various molecules. The devices require expertise to read, and Guard members were just learning to handle them.

"Interpreting the plot lines is challenging," said Army 1st Lt. Thomas Benton, a New York Guard member. "Analysts typically have had PhDs and a lot of high-level chemistry."

During one practice session, recalled Army Maj. Robert Domenici, the New York team leader, "It took us several minutes to realize that what we were monitoring was gasoline."

But for the most part, military and industry specialists observing the exercises expressed satisfaction with the Guard units.

"The training has been pretty intense, but we're getting there," said Army Staff Sgt. Tim Riley, whose job as a "modeler" for the Missouri Guard is to estimate the danger zone around a chemical or biological attack. "For the time we've been allotted and everything, we're probably ahead of the power curve."