Already battered by questions about the safety and effectiveness of its 1 1/2-year-old effort to inoculate all U.S. troops against anthrax, the Pentagon faces new evidence suggesting that some vaccinations are not being administered on time, particularly to reservists.

Military vaccination records obtained by a House panel show that nearly half of the 32,000 National Guard and military reserve members inoculated so far were overdue for the required additional shots. Delays in administering the vaccine, which involves an unusually extensive regimen of six shots over 18 months, can retard its efficacy.

Defense officials dispute the numbers, saying the problem lies more with slow reporting by the Pentagon's central tracking system. But they acknowledge some difficulty in delivering the inoculations because of part-time training schedules or out-of-town travel.

With Congress weighing two bills that would either suspend the inoculations or make them voluntary, the latest disclosure promises to generate fresh questions about the wisdom and management of the vaccination program--the Pentagon's first attempt to protect the entire military against a germ warfare agent.

Rep. Christopher Shays (R-Conn.), who chairs the national security panel of the House Government Reform Committee, intends to focus on the vaccination compliance data at hearings today. And a House Armed Services panel has scheduled testimony for Thursday to review the program.

While determined to continue the vaccination effort, the Pentagon finds itself increasingly on the defensive. Touted initially by military officials as a far-sighted response to the rising threat of germ warfare, the program has become a source of some unrest in the ranks and political controversy on Capitol Hill.

The 220 troops who have openly resisted the vaccine constitute only a tiny fraction of the 350,000 service members inoculated so far. But the fact that even that many are willing to accept expulsion from the military for refusing the shots suggests a broader undercurrent of unease among military families worried about possible adverse reactions to the vaccine. Some of the most pronounced opposition has come from reservists, who are freer to quit the military.

"The message we've been sending the Pentagon is that you have to pay attention to the concern; you can't just tell troops to take the vaccine because you told them to," said Rep. Steve Buyer (R-Ind.), who heads the Armed Services subcommittee on personnel.

At an internal strategy meeting called last month by Deputy Defense Secretary John J. Hamre, Pentagon officials conceded that more should have been done to explain the program to service members, according to several participants.

"Science is not winning this debate; emotion is," said a senior officer who attended the meeting.

Hamre has ordered stepped-up efforts to educate troops about the need for the vaccine and to dispel fears of side effects. He also has sought greater involvement by four-star regional commanders in selling the program.

Anthrax tops the U.S. government's list of biological warfare threats because it is considered the easiest germ weapon to make and use. When inhaled as tiny, dry particles, it can cause severe pneumonia and death within a week.

Although no country is known to have released the bacteria on a battlefield, the Pentagon has called attention to Iraqi attempts to stockpile anthrax supplies and estimates that at least 10 countries have developed germ weapons. In December 1997, Defense Secretary William S. Cohen ordered all 2.4 million active duty and reserve troops vaccinated, starting with those serving in the Persian Gulf or South Korea or in units likely to be called into combat.

The vaccine has existed for three decades. It was approved for use by the Food and Drug Administration in 1970, largely for veterinarians and others who work with livestock or animal products. But critics note that much more is known about the vaccine's ability to protect against cutaneous anthrax, the usually nonlethal form that attacks the skin, than about the form of anthrax that might be inhaled on a battlefield.

In launching the inoculation program, Cohen insisted that the military services keep close track of the shots. The Pentagon set up a monitoring network, known as the Defense Eligibility and Enrollment Reporting System, or DEERS. It was in culling through DEERS data that Shays's staff discovered what they say is an alarmingly high percentage of reservists overdue for shots.

In some cases, entire reserve units had missed the inoculation schedule by a month or more, the House panel found.

Charles Cragin, the Pentagon's assistant secretary for reserve affairs, said yesterday that the DEERS data gave a misleading picture of compliance because of a lag in service reports. "Many of the overdues are really the result of tardiness in reporting rather than any sort of delay in the vaccinations," he said.

But Cragin, who is due to testify today, acknowledged that some reserve units were falling short of the standard: administering 90 percent of the shots within 30 days of their due date. The reserves' compliance rate is between 70 percent and 90 percent, Cragin said.

Overdue Inoculations

Many reservists and Guard personnel are not meeting the timetable for getting their six anthrax vaccine shots.

Anthrax vaccinations

Air Force Reserve

Participants: 8,931

Overdue: 2,954

Air National Guard

Participants: 9,246

Overdue: 2,482

Army National Guard

Participants: 2,441

Overdue: 1,443

Army Reserve

Participants: 5,802

Overdue: 3,661

Marine Corps Reserve

Participants: 2,730

Overdue: 1,967

Navy Reserve

Participants: 3,531

Overdue: 3,118

SOURCE: House of Representatives

CAPTION: Senior Chief Petty Officer John Payhurst administered anthrax vaccinations aboard the carrier USS John C. Stennis while it was in the Persian Gulf in 1998.