The Defense Department's deputy inspector general said yesterday that the Pentagon buys billions of dollars' worth of weapons without knowing whether they will work because officials are not willing to wait for accurate tests or to explain unfavorable results to their superiors.

Derek J. Vander Schaaf, testifying before a Senate Governmental Affairs subcommittee, agreed with a General Accounting Office report released yesterday that said Pentagon arms testing is inadequate. But he said an independent testing office now sought by 17 senators will not by itself solve the problem.

"The proposed new office would still not be able to provide adequate test results to decision makers unless dramatic steps are taken to correct the four major shortcomings I mentioned earlier," Vander Schaaf said.

Those shortcomings include decisions to buy weapons before they have been fully tested, involvement of weapons manufacturers in the testing of their own products and withholding of weapons test results from top officials.

"The potential importance of test restrictions and limitations were not always explained to decision-makers," Vander Schaaf said.

Senators complained that they receive even less information than top Defense officials from testing offices in the Army, Navy and Air Force. Sen. Warren B. Rudman (R-N.H.) said data sheets the Pentagon is required to send Congress on weapons makes all of them look "like peaches and roses."

"It's probably wishful thinking to hope you could get all of the weaknesses put in those reports," said Isham Linder, the retired admiral in charge of reviewing the data sheets as director of the Pentagon's office of test and evaluation.

Linder appeared before the subcommittee to respond to GAO charges that the Pentagon has ordered weapons worth at least $33 billion without knowing whether they will work in a war.

Linder reports directly to the Pentagon's research director, Richard D. DeLauer, a situation that Sen. William V. Roth Jr. (R-Del.) charged was certain to compromise his independence. Linder disagreed yesterday and said the Pentagon's testing system "yields the kind of answers on current systems that are needed."

DeLauer decided late Wednesday afternoon not to testify as scheduled, and attempts to reach him yesterday were unsuccessful. In an ABC television interview early yesterday, however, he dismissed the GAO criticism and the proposal to create an independent testing office.

"It seems to me there's some misinformation in regard to the performance of our weapon systems," DeLauer said. "Remember, it's a development process, and most of the weapons which are mentioned in this GAO report right here are still under development."

But the Pentagon has committed itself to buying many of the weapons even while they are under development, according to Vander Schaaf's report, in order to hasten their availability.

The Navy, with congressional approval, decided to purchase eight Aegis-class cruisers, which cost almost $1 billion each, before any sea trials and "before it was shown that the ship was capable of meeting Navy mission requirements," Vander Schaaf said.

Similarly, the Bradley armored fighting vehicle was well on its way to production when tests first showed that the presumably amphibious vehicle would not float, he said.

"Certainly the flotation failed and the thing would have sunk," Linder said. "I expect that those will be shown to be fixed as we get to the field tests that are just about to start."