The Defense Department has grown out of control and must be overhauled at the top to provide more centralized direction and accountability, according to a report to be released soon by the Senate Armed Services Committee.

The report comes as President Reagan's rearmament program is being challenged by Republicans and Democrats in Congress and by other critics.

The House Armed Services Committee, for example, is holding hearings to assess what the nation received for its expenditure of$1 trillion on defense during Reagan's first term.

Defense Secretary Caspar W. Weinberger, in what had been billed by the Defense Department as a major policy speech, attempted to define the administration's defense strategy in an appearance before the National Press Club yesterday.

But he stuck to generalities, rather than address specific criticisms made recently in speeches on the Senate floor by Armed Services Committee Chairman Barry Goldwater (R-Ariz.) and the panel's ranking Democrat, Sam Nunn (Ga.).

Weinberger said that the Carter administration, in spending too little on defense, "appeared to have settled for a strategy of dangerous deterrence."

He defined the Reagan administration's defense policy as an effort "to build the strongest possible deterrent as quickly and effectively as possible.

"To be effective, our deterrent must . . . credibly persuade Soviet leaders that they have no significant exploitable military advantages against our vital interests and . . .minimize the risk of failure through accident, unauthorized use or miscalculation by the Soviets," he said.

Weinberger declined during the subsequent question-and-answer session to go beyond such generalities and address specific problems spotlighted in the Senate Armed Services Committee study, on which he had been briefed.

Although the Senate report has not been made public, its main thrust is that the Defense Department is broken and must be fixed, according to people who have read the report.

It blames no single defense secretary but says the problems have accumulated, many of Congress' making. They imperil the armed forces' effectiveness in a future war, the report said.

One of many reforms recommended in the report, sources said, would give the chairman of the Joint Chiefs of Staff more independence and power. He no longer would have to reach unanimous agreement with all four armed services chiefs before presenting military advice to the president.

Goldwater, Nunn and other committee members met with a wide spectrum of military leaders at the Army's Camp A.P. Hill in Virginia last weekend to discuss the report's major findings.

Retired admiral Thomas H. Moorer, a former chairman of the Joint Chiefs, opposed changing the Joint Chiefs' organization, participants said, but other military leaders at the meeting agreed that changes are needed.

John Collins, a senior defense specialist at the Library of Congress, told a House Armed Services Committee panel yesterday that the $1 trillion spent on defense under Reagan has kept the nation's nuclear deterrent from eroding, "but it did not increase combat capabilities that much if deterrence fails."