The Pentagon encountered only light fire yesterday as the Senate voted, 77 to 21, to authorize $178 billion to buy almost all of the weapons President Reagan requested for fiscal 1983.

But Joseph P. Addabbo (D-N.Y.), chairman of the House Appropriations subcommittee on defense, warned that the Defense Department would encounter more difficulty when his subcommittee considers recommending how much of the authorized money should be appropriated.

"We must face the hard, cold facts of reality," Addabbo told Defense Secretary Caspar W. Weinberger, who appeared before the subcommittee yesterday. Addabbo said ways must be found to cut about $10 billion from the Pentagon budget to help lower the soaring federal deficit.

Addabbo pleaded with Weinberger to suggest defense budget cuts "so we won't be wasting money." But Weinberger insisted that the administration has trimmed its original defense bill as much as it dares, considering the Soviet threat.

"Since we presented our original program," Weinberger testified, "we have confirmed significant additions to the Soviet inventory and positively identified several new Soviet weapons."

He said the Soviets have produced 65 more SS20 mobile, intermediate-range missiles, bringing the total to 315; flight-tested the Blackjack A long-range bomber, which is "slightly larger than the B1 and will probably be operational by the mid-1980s," and deployed 60 more Backfire bombers for a total of 200.

The final authorization bill worked out in a House-Senate conference sets money ceilings for various weapons. The appropriations committees usually recommend amounts under the ceilings.

Sen. Carl Levin (D-Mich.) complained yesterday that ceilings set by the House and Senate armed services committees are so high that those committees are making themselves irrelevant to the congressional budgeting process.

Saying that his figures were based on Congressional Budget Office calculations, Levin said the final authorization bill passed yesterday by the Senate would push the fiscal 1983 defense budget $500 million in budget authority and $3 billion in spending over goals established in the Senate budget resolution.

John G. Tower (R-Tex.), chairman of the Senate Armed Services Committee, predicted that cuts in other defense bills, particularly military construction and pay, would keep the authorization bill from breaking the resolution ceilings.

The $178 billion authorized in the final bill, which must be approved by the House, is higher than totals approved by the Senate and House originally. The Senate had authorized $177.4 billion and the House $175.3 billion.

Sen. Gary Hart (D-Colo.) said it is "appalling" that the final defense bill exceeded those passed originally by the Senate and House.

Tower and Sen. John C. Stennis (D-Miss.), ranking Democrat on the Armed Services Committee, contended during yesterday's debate on the conference report that the Soviet threat and the need to strengthen the hand of arms negotiators demanded the record-high peacetime defense bill.

But the debate was dominated by critics of the bill, including several members of the Armed Services Committee who urged that the measure be returned to conference for a rewrite.

"It perpetuates and reinforces the highly questionable presumption that throwing gobs of money at the problem is sound defense policy," Sen. J. James Exon (D-Neb.) said of the bill.

Exon deplored rushing toward the MX deployment scheme called "Dense Pack," which calls for placing the missiles closely together, without conducting congressional hearings to assess the impact on the SALT II arms control agreement and the antiballistic missile treaty.

"We've had no hearings on Dense Pack . How can we possibly rush headlong at this stage?" Exon asked during the floor debate.