The United States is producing billions of dollars worth of weapons without knowing whether they can do the job because they have not been adequately tested, according to a General Accounting Office report scheduled to be released today.

The report says the Defense Department for years has acknowledged the problem in internal reports but never has taken the necessary steps to correct it. In addition, many Pentagon officials are in charge of both developing and testing specific weapons, leading to "conflicting interests" and lax tests, the report says.

"Too often, the attitude is, 'Buy it now, Band-Aid it later,' " said Sen. William V. Roth Jr. (R-Del.), whose Governmental Affairs oversight subcommittee will hold hearings on weapons testing this morning.

"The result has been that more than $33 billion in weapons systems are now in production whose safety, reliability and combat readiness remain unproven."

According to the GAO, Congress' investigative and auditing agency, the $33 billion is probably an understatement. It represents the cost of only 10 weapons programs the GAO examined in its current report.

The report says that, as weapons become more expensive and technologically sophisticated, testing requirements do the same. But Pentagon officials often fund hardware at the expense of test resources, which the GAO calls "easy candidates for budget reductions and schedule delays."

The Pentagon aims to simulate battlefield conditions when it tests new weapons, but the report says tests have not kept pace with technological improvements in Soviet and other weapons. The Air Force and Navy test their missiles, for instance, against dummy aerial targets that are slower and less maneuverable than modern Soviet jets.

Similarly, the Air Force is spending $3.6 billion for a new electronic system for the B52 to reduce the bomber's vulnerability to Soviet radar and missiles. The new "avionics" are intended to help the bomber penetrate Soviet defenses and guide its new air-launched cruise missile to its target, but they have never been tested against realistic simulations of Soviet radar, the report said.

"Since test and evaluation has not shown that the system will be operationally effective, the Air Force will deploy a new avionics system that may not work and may require an expensive modification program in the future," the GAO said.

The Defense Department rejected GAO criticism yesterday and in responses to the report. Officials there "contend that although testing may not be complete, it is adequate," the report says.

Sen. David H. Pryor (D-Ark.) disagrees and has proposed legislation, now endorsed by 17 co-sponsors, to establish an independent testing office within the Pentagon. The department opposes the proposal as unnecessary.

Pryor said yesterday that both Pentagon and industry officials have "a conflict of interest" when they test the weapons they also are developing.

"It's like a student grading his own exams," Pryor said. "The industry is part of the testing, and I think that presents a serious problem in the quality of weapons and the cost of weapons."