The furor over the Soviet Union's downing of a South Korean airliner has at least temporarily strengthened President Reagan's hand in dealing with Congress on defense and related national security issues, a broad array of Republican and Democratic lawmakers said yesterday.

But some questioned whether Congress will translate its outrage into a new surge in defense spending, and most said any long-term, fundamental shifts in congressional attitudes are likely to hinge more on future Soviet behavior than on this one incident.

Among about 15 legislators who were interviewed yesterday, mostly members of defense-related committees of the House and Senate, a vast majority voiced support for the president's handling of the situation, especially his emphasis on an international response.

They also were ambivalent as to how Congress should respond to the killing on Monday of two more Marines in Lebanon, after the deaths of two others there last week. While some said the administration should consider seeking congressional authorization under the War Powers Act for continued deployment of U.S. forces there, few appeared willing to initiate congressional action on their own.

It was generally agreed that the Democratic-controlled House, where some key defense issues have been decided by relatively close votes, is likely to feel more of an impact from the Korean airline disaster than the Republican-controlled Senate, where Reagan has a comfortable margin on most defense issues.

Congress faces votes on several major defense measures shortly after it returns from its five-week summer recess Monday, including a conference report on the defense authorization bill and the defense appropriations bill, both of which involve the controversial MX missile.

The Senate also faces a nuclear freeze resolution, and several senators, including Sen. William Proxmire (D-Wis.) as well as several Republicans, said already dim prospects for the resolution are probably even dimmer.

Several lawmakers, including the chairmen of the House and Senate Appropriations subcommittees on defense, said they believe that support for the MX will be stronger than it was before the Soviet attack.

"That's a big, visible vote and you can say, 'Well, I got back at the Russians, I voted for this MX,' " said Rep. Joseph P. Addabbo (D-N.Y.), chairman of the House Appropriations subcommittee on defense.

Sen. Ted Stevens (R-Alaska), chairman of the counterpart Senate subcommittee, said he thought an appropriation for the MX would be approved by roughly the same 17-vote margin by which the Senate voted to authorize the missile in July, although he previously said he thought the MX money would squeak through by one or two votes.

As for defense spending in general, "the effect will be that it probably will cause the defense budget to be a bloated mess again," Addabbo said.

"There's no logic to it, but I would imagine people are going to try to fool the American people by voting for some big defense projects and saying they're getting back at the Russians," Addabbo said. "You don't fool the Russians, because they read these technical journals, and they know the money is going into planes that don't fly and ships that don't work.

"It obviously strengthens the president's hand for about 30 days . . . . The question is how much longer," said Sen. Dan Quayle (R-Ind.), a member of the Senate Armed Services Committee.

Rep. Les Aspin (D-Wis.), a senior member of the House Armed Services Committee and key figure in marshaling Democratic support for the MX, agreed that Reagan's position on both defense and arms control, including the MX, will be strengthened for the short run. But, he noted sardonically, Congress "has an institutional memory of about 6 months."

On arms control, said Aspin, "It'll buy him time; it doesn't get him off the hook. He's still got to come up with an arms-control proposal that moderate people on both sides say is a serious thing."

Said Sen. John W. Warner (R-Va.), chairman of the Senate Armed Services subcommittee on nuclear forces: "In all likelihood there will be stronger support for defense , but I hope that support will not be in the direction of appearing to propel us into an arms race."

"The momentum on defense issues is going to move the president's way," said Rep. James A.S. Leach (R-Iowa), a member of the Foreign Affairs Committee.

Several lawmakers, including Senate Appropriations Chairman Mark O. Hatfield (R-Ore.) and several Democrats, doubted that the Korean air disaster would have much of any effect on defense votes, largely because it was not a crisis that required military response.

Sen. Carl Levin (D-Mich.) said, for instance, that opposition to the MX arises from the question of "whether we'd be stronger with it or without it."

Rep. Stephen J. Solarz (D-N.Y.), a Foreign Affairs Committee member, said: "It the impact of the air disaster will be marginally helpful to the president, but I don't think it will mean a permanent change in congressional attitudes. The results will be seen on some specific systems, where the vote will be sending a message.

As for the Senate, "The president gets what he wants out of here anyway," Proxmire said.

But even Senate Republicans did not suggest that Congress would go back on its earlier decision to cut Reagan's military buildup for the fiscal year starting Oct. 1 from 10 to 5 percent.

"Nobody's talking about going back to 10 percent," said a GOP leadership aide.

More likely, said Sen. Warren Rudman (R-N.H.), a member of the defense appropriations subcommittee, are votes to increase readiness of fighting forces, such as increased outlays for ammunition and training.