The Defense Department has replaced its contract-fraud team in recent weeks, raising questions in Congress about the Pentagon's commitment to combating weapons-procurement abuse.

Congressional aides said the five agents of the Contract Fraud Division had criticized top Defense and Justice department officials for not aggressively investigating and prosecuting alleged fraud by defense contractors. One of the agents resigned, and four were transferred.

A Pentagon spokesman said three of the agents were transferred at their request and the fourth was moved to avoid a potential conflict of interest. He said the unit will be filled by "highly qualified, fraud-trained agents."

The shakeup comes amid intense congressional scrutiny of military procurement practices inspired by reports of runaway cost overruns on weapons systems and questionable contractor charges for spare parts and administrative activities. The division, part of the Pentagon's inspector general's office, oversees procurement-fraud investigations by field agents and helps the Justice Department prepare prosecutions.

Sen. Charles E. Grassley (R-Iowa), in a letter last week to Inspector General Joseph H. Sherick, said he is concerned that "the sudden transfer" of the agents "may adversely affect the government's efforts against fraud."

Rep. John D. Dingell (D-Mich.) said the shakeup "shows that the Pentagon's talk of aggressively investigating wrongdoing on the part of the major defense contractors is more talk than substance."

Dingell, whose House Energy and Commerce oversight and investigations subcommitee has uncovered several cases of procurement abuse, said the shakeup will weaken Sherick's ability to probe fraud and will give defense contractors "cause to celebrate."

The staff changes, which began last month, were reported Sunday by the St. Louis Post-Dispatch.

All five agents had been hired by Brian Bruh, who left his job as director of the Defense Criminal Investigative Service (DCIS) in December after complaining that Pentagon and Justice Department officials were lax in probing contract fraud, sources said. Jerry Strickler, who headed the contract-fraud division since early 1982, was transferred to an administrative job in DCIS headquarters after indicating that he planned to leave government, perhaps for a job that could involve a conflict of interest, a Pentagon spokesman said.

Another agent was sent to the headquarters, and two went to field offices, sources said.

Bruh's successor, Bertrand G. Truxell, who is said to have directed the personnel shifts, did not return telephone calls yesterday.

Another defense official said the former staff was old-fashioned in investigative techniques, pressing for criminal investigations of contractors instead of accepting equally effective plea arrangements.