A House-Senate conferees' compromise to authorize $187.5 billion in military spending for next year won emphatic final approval from the Senate yesterday in the first congressional action on defense policy since a Soviet warplane shot down a South Korean airliner two weeks ago.

The vote was 83 to 8, with most Democrats joining all Republicans in attendance in voting for the measure.

It now goes to the House, where its prospects are less clear.

The bill, which would authorize production of nerve gas weaponry for the first time since 1969 and give the go-ahead for the controversial MX missile, was passed amid frequent references to the Soviet downing of the Korean plane.

"I can think of no other period in the recent past that more vividly demonstrates the dangers we face," said Senate Armed Services Committee Chairman John G. Tower (R-Tex.) in arguing that the plane disaster and other events during the congressional recess had powerfully strengthened the case for Reagan's military buildup.

Sen. David H. Pryor (D-Ark.), who had fought against the nerve gas authorization but voted for the bill, said sardonically that he hoped that nerve gas would not stand as "our monument to the 269 dead people who did not survive the Korean airline tragedy."

Pryor said he was withholding another fight over nerve gas "at this very emotional time" and would wait "until our perspective is a little better."

While Senate approval of the defense compromise had been expected even before the airliner disaster, the Soviet attack appeared to have dampened efforts to trim defense spending and cut out controversial weapons programs, which had tied the Senate in knots for several weeks during the summer.

The bill faces its biggest hurdle in the House, where more than 70 members have signed a letter calling for its rejection.

Especially because of the nerve gas authorization, which the House had previously rejected, the measure has been expected to encounter stiff opposition among House members who were already uneasy over the MX missile.

But some members have said the outraged response to the Soviet attack on the airliner could produce enough votes for passage when the bill comes to the House floor, probably later this week.

"The climate has changed; the question is how much," said one House aide.

Among the Democratic presidential contenders in the Senate, John Glenn (Ohio), Alan Cranston (Calif.) and Gary Hart (Colo.) were not on hand for yesterday's vote.

Hart had led the earlier Senate effort to kill production funds for the MX missile.

The only presidential candidate who voted yesterday was Sen. Ernest F. Hollings (D-S.C.), who joined Democratic Sens. Edward M. Kennedy (Mass.), Patrick J. Leahy (Vt.), Carl Levin (Mich.), Howard M. Metzenbaum (Ohio), Claiborne Pell (R.I.), William Proxmire (Wis.) and Paul E. Tsongas (Mass.) in voting against the bill.

All Washington-area senators voted for the measure.

The bill is generally in line with an earlier congressional decision to cut by half Reagan's proposed 10 percent after-inflation increase in defense spending for the 1984 fiscal year starting Oct. 1.

But it would give him virtually every weapons system he wanted, including $4.8 billion for the MX missile, $5.6 billion for the B1 bomber, $430 million for Pershing II missiles that are to be deployed in Europe shortly and $144.6 million for nerve gas weapons.

To satisfy objections in the House, the number of MX missiles was reduced from 27 to 21 and their deployment was tied to development of a smaller, more mobile missile favored by arms control advocates.

Also, the final assembly of nerve gas weapons was delayed until Oct. 1, 1985, as the Senate had recommended.

The Senate had approved resumption of nerve gas production by a one-vote margin only after Vice President Bush broke a tie vote.