WASHINGTON (AP) _ The Pentagon's inspector general, citing more than $1 billion in questionable spending, says the military should slow down its construction projects until after the 1995 round of base closings.

''Every military construction project in the Department of Defense is suspect,'' Derek J. Vander Schaaf told a Senate panel Wednesday. ''We ought to be very careful and go slow.''

Vander Schaaf said Pentagon auditors have found $1.4 billion in questionable spending on building projects over the past 2 1/2 years. Separate reviews by auditors from each military service have raised questions about an additional $800 million in construction.

Appearing before the Senate Governmental Affairs Committee, Vander Schaaf said the military sometimes provides no justification for the projects or does an incomplete job. Lawmakers seeking pork barrel dollars contribute to the problem by funding questionable projects not requested by the Pentagon, he said.

Vander Schaaf stopped short of endorsing a complete stoppage of military construction, saying some projects were vital. But he said, ''Military construction spending should be minimized until the (base closure) process has run its course.''

Taxpayers are particularly susceptible to financing projects conceived years ago for bases now slated to close.

''Unrealistic assumptions go unchallenged or, in what may be the most likely scenario in this era of rapid downsizing, originally sound planning assumptions are overcome by events, but are not revisited after the project proposal goes forward,'' Vander Schaaf said. He cited several examples:

-In 1989, the Navy committed $368 million for 1,183 family housing units at Naval Station New York on Staten Island. The apartments were needed for crews of battleships that would be stationed there. But the battleships were retired from the fleet in 1990 and the base was scheduled to close in 1993.

Vander Schaaf said the Navy was left with a ''contractual mess,'' because the contract had no termination clause.

-Pentagon auditors questioned a $240 million project to build a new rocket test facility at the Arnold Engineering Development Center in Tullahoma, Tenn. The auditors challenged arguments that the facility was needed to improve safety at the testing center. ''Nevertheless, there was strong congressional support for the project and the Air Force refused to change its safety assessment,'' Vander Schaaf said. He added that he ''will be interested to see how often the facility is actually used.''

-Despite a Pentagon assessment that a proposed new Fitzsimons Army Medical Center near Denver was unnecessary, Congress approved $300 million for it.

-Reviews of construction ordered because of base realignment decisions since 1988 turned up $233 million in questionable projects.

In a separate report to the committee, the General Accounting Office, Congress' investigative arm, said the Navy may have wasted as much as $33 million on a long-term lease for research space in Suffolk, Va., just as it learned that most of the research would be transferred to a base in Rhode Island.

Over the past five years, committee members said, Congress has added $4.4 billion in unrequested military construction to the defense budget.

Last month, the House approved an $8.8 billion military construction budget that exceeded President Clinton's request by $470 million. And the Senate began consideration Wednesday of the Senate Armed Services Committee's draft of the 1995 defense budget, which would add $282 million for military construction to Clinton's request.