Washington — The plan for the MX missile no longer looks like a Rube Goldberg invention. But if President Reagan is to gain congressional approval for the latest plan to find a home for the much-debated MX, it will require a crazy-quilt, Rube Goldberg-style political coalition.
The MX has been on again, off again through four administrations. Last December, Congress refused to approve production funds for the missile. Mr. Reagan appointed a high-powered bipartisan commission to take a new look at basing plans for the missile. On April 11, the head of the commission, Brent Scowcroft, a former White House national-security adviser, is expected to formally present the latest basing plan to Reagan in a report probably fewer than 50 pages long.
Unlike some complicated proposals of the past - which have included the so-called dense-pack, Big Bird, and race-track proposals, all beloved of cartoonists - Mr. Scowcroft and his colleagues are proposing that the MX simply be placed in 100 existing but hardened missile silos.
The longstanding problem has been to find a way of basing the MX missiles in a way that would allow them to survive a nuclear attack and then be fired in retaliation. The latest proposal is only an interim step. It does not solve the survivability problem.
But the commission is also going to be calling for further study of other means of deploying the MX. And it is going to recommend research and development work on a new small, single-warhead missile - an idea that has gained considerable popularity in the Congress and elsewhere in recent years. Supporters say the single-warhead missile might prove to be less destabilizing to the nuclear balance of power than the 10-warhead MX.
Reagan is expected to accept the recommendations. But he will need all the help he can get in trying to win approval for deploying the missile, including that of Democratic liberals. No one is really happy with the Scowcroft commission plan, but there is something in it for everyone - including some of the Democratic liberals who are so often at odds with the White House.
One key liberal and nemesis of the Pentagon, House Armed Services Committee member Rep. Les Aspin (D) of Wisconsin, is said to be leaning in favor of the Scowcroft plan. If a hard-nosed critic of defense budgets such as Representative Aspin goes for the new plan, it could influence others.
Aspin's thinking, according to an aide, is this: It is time to reach a new consensus on defense spending, and to avoid sharp increases or cuts - feast or famine - in defense programs. Most Americans favor a modest increase in defense spending as well as some form of arms control. The proposed 100 MX missiles will not be numerous enough to threaten the Soviet Union's land-based missile force but might be numerous enough to nudge the Soviets toward negotiation.
In return for that, liberals get research and development on the single-warhead missile. The development of this missile would mean a shift in strategic policy away from large, multiwarhead missile systems, which are both vulnerable and threatening at the same time, liberals say.
Aspin is said to hope that the bipartisan, pragmatic attitude that characterized the recent enactment of social security reforms will be at work when it comes to the controversial MX and the smaller, single-warhead missile.
One problem, liberals readily admit, is that many in the Pentagon are not really enthusiastic about the smaller missile, dubbed ''Midgetman.''
The idea is coming too late in the game, one high-ranking Defense Department official recently told a reporter. He added that to make the Midgetman mobile, if that became necessary, would cost too much.
''The Pentagon doesn't like anything that's small,'' said Rep. Joseph P. Addabbo (D) of New York, chairman of the House defense appropriations subcommittee.
Representative Addabbo, who headed a House coalition that blocked MX production funds in December, says he favors research into the small missile but still opposes the MX. He says that with new liberal Democrats in the Congress, he and colleagues can again defeat the MX.
''If they get 100 MXs, that just opens the door to more,'' says Addabbo, who believes the multibillion-dollar MX system will never be invulnerable to attack. ''The new plan is really no different from what we've had before. It's just back to Plan 1.''
But another key MX opponent, Rep. Norman D. Dicks (D) of Washington, agrees with those who say that with a 100 MX-Midgetman combination, Reagan will be much more difficult to defeat this time. Representative Dicks also argues, however, that many of his colleagues do not really believe Reagan is serious about arms control. This makes them skeptical of anything Reagan proposes in the way of nuclear weapons production, Dicks says. He adds that Reagan's recent suggestion that new defensive technologies, possibly using space-based X-ray lasers, might be used to block incoming Soviet missiles just created more mistrust of Reagan.
''That's the one that really blew me away,'' says Dicks. ''It just creates a new arena for the arms race.''
The controversy over the President's choice of Kenneth Adelman to head the Arms Control and Disarmament Agency also is working against the administration. Many liberals contend that Mr. Adelman lacks the background and seriousness about the subject to be involved in arms control negotiations.
Then there is what might be termed the Rube Goldberg factor. The MX has gone through so many permutations - more than 30 basing modes have been considered - that there is a tendency to laugh at it. In discussing the projected small missile, and an armored truck called an ''armadillo'' that might be used to transport it, one defense expert pleaded with reporters not to call the combination ''Midgetman and armadillo.'' He not so jokingly suggested that such cartoon-like terminology could cost the administration 30 percent of the vote on the MX.
Working in favor of the Scowcroft commission on Capitol Hill is the personality of Scowcroft himself. He is a moderate Republican and former Air Force general who, according to all accounts from Congress and from within the commission itself, has an extraordinary ability to forge compromises. The feeling on Capitol Hill and in the commission is that if Scowcroft can't win this battle, no one can.