Congress must decide whether the MX missile system will fly. Members returned to post-election Washington to a debate with ramifications that involve the world.
To President Reagan's charge that ''in virtually every measure of military power the Soviet Union enjoys a decided advantage'' comes Moscow's counter-declaration. The MX is a ''first strike'' weapon, says Soviet news agency Tass, and with it, Reagan has proposed ''a new, dangerous step'' in the arms race.
As Congress begins deliberations on the MX, observers say the outcome will be close. Many members say they feel an obligation to support the President in an international, albeit rhetorical, dispute with the Soviet Union. On the other hand, some point to the US peace movement with its ''freeze'' proposals. Is the MX plan merely a ''bargaining chip'' to force concessions from the Russians at future arms control talks, they ask?
Unlike the historic decision against the League of Nations ratification in 1919, which was debated in the Senate alone, this policy question involves both chambers of Congress because it requires approval of House-controlled money bills. These would finance Reagan's proposed deployment of 100 MX intercontinental ballistic missiles in a dense-pack configuration in Wyoming.
The lame-duck session of Congress is expected to last about three weeks. It could make major appropriation policy decisions - decisions the 86 new faces in the 98th Congress would have to live with. The President wants $248 billion for his 1983 defense program, which includes $4.3 billion for continued development of the MX system using the basing plan he announced in a televised speech Nov. 22.
But congressmen do not deny that America's finances will play a role in their decision. House and Senate Republican leaders have warned the White House that the military budget will be under almost irresistible pressure for cuts. Cost considerations weigh even more heavily under speculation that the MX plan eventually will need to be protected by an antiballistic missile (ABM) system. Deployment of an ABM system could double the price of the dense-pack system, experts say.
The dense-pack plan would locate 100 missiles in a narrow strip just outside Cheyenne, Wyo. Defense depends on the unverified theory that attacking Soviet weapons would be unable to destroy all of the MX missiles and would in fact be self-destructive, setting off explosions that would block succeeding Russian missiles. Theoretically, the delay would permit the US to get off counterattacks.
Congressmen are rubbing their eyes. Seldom in history has a legislature been asked to vote on such nightmarish, technical issues.
One hopeful sign is that the US and Soviet Union have so far abided by the terms of the SALT II arms limitation agreement, even though the US has not ratified the treaty. Whether compliance would continue under the MX missile program is uncertain.
Returning congressmen gave preliminary statements, but most remain cautious and reserve judgment. They seem awed by the issue, and the outcome is doubtful as the session gears up.