For nearly 10 years, the MX missile has been the prime symbol of progress in United States strategic nuclear capability. At the same time, however, its formative years have been almost exclusively political - a fact sharply evident this week in Washington, where officials are deciding whether to begin building and deploying this new generation of US nuclear arms.
Two months ago, House and Senate liberals and conservatives in large measure signed off on the recommendations of a presidential commission to deploy 100 MXs in existing missile silos, develop a small single-warhead missile, and shift arms control efforts to a more stabilizing stance.
There has been perceptible progress on the Scowcroft Commission's latter two points, which were seen as the cost to the Reagan administration of winning the MX. But Congress still has great difficulty going over the top on MX production and deployment. If anything, the balance of support has shifted back toward the anti-MX side of the debate.
Why do lawmakers still hesitate? There are serious questions about cost. Many experts, including Gen. Maxwell D. Taylor, former chairman of the Joint Chiefs of Staff, still question the MX's military necessity. Antinuclear and other activists continue to chip away at public opinion. Environmentalists have sued Defense Secretary Caspar W. Weinberger for not following US law in checking the environmental impact of MX deployment.
Mr. Weinberger Monday summoned reporters to emphasize that the administration is ''totally and completely dedicated to the Scowcroft recommendations.'' That he felt it necessary to do so illustrates the political complexity of the issue: There still is little love for the missile itself on Capitol Hill except as an arms control bargaining chip - as much between Congress and the White House as between the US and the Soviet Union.
Rep. Les Aspin (D) of Wisconsin, a principal Scowcroft Commission water carrier on Capitol Hill, notes, ''There is no consensus on a way to base MX. . . . Every basing system has at least half the people against it.''
Writing in the Washington Post this week, General Taylor argued that ''the missile would add little if anything to the survivability or deterrent effectiveness of our strategic forces.''
And although there is growing agreement that the US should shift away from large, multiwarhead missiles in its land-based strategic force, the cost of replacing them with the ''Midgetman'' is very large. The Air Force puts the price of building and deploying 1,000 of the single-warhead missiles at $70 billion - nearly three times the projected cost of the total MX program. The Congressional Budget Office says Midgetman's price tag would be closer to $100 billion.
Because domestic programs have been cut substantially relative to defense, cost is also an important factor to MX opponents. The Center on Budget and Policy Priorities, a liberal New York public-policy research group, this week reported that canceling MX outlays for 1984 ($1.75 billion) would allow restoration of funds for social programs including the Work Incentives Program, Legal Services Corporation, Health Services Administration, Low-Income Energy Assistance, Job Corps, Child Welfare Services, and others. Of the projected $24 billion cost of the MX, defense analyst Gordon Adams, who directed this study, says ''My sense is, it's almost bound to be an underestimate.''
As part of its effort to win the first 27 MX missiles next year, the administration has been working very hard to demonstrate its earnestness to develop the Midgetman. It has acceded to a defense authorization bill amendment written by Representative Aspin that would tie MX deployment to small missile development and restrict the size of Midgetman. But, keeping in mind environmental questions raised by earlier MX deployment schemes, the Pentagon wants to keep the smaller mobile missile (as it does the MX) on existing military property.
This may not assuage environmentalists. A federal lawsuit brought by Friends of the Earth charges that the Pentagon must not only report on the environmental impact of MX deployment, but must say what the ''worst case'' result would be of accident or actual nuclear exchange.