Washington — Few decisions are tougher for Congress than passing judgment on the MX missile system. Against a backdrop of increased world tension, the members see the nuclear freeze movement and economic woes in their districts as they consider paying up to $40 billion during this decade to construct and operate the giant new weapon.
Even hawks are saying they would like to see the missile bargained away at arms control talks, much as the Anti-Ballistic Missile system has been limited by negotiations.
''It's my hope that the system will never be built,'' said Sen. Henry M. Jackson (D) of Washington, after meeting with the President. A longtime friend of the military, he said he's ''reserving judgment on a basing mode'' for the MX , which the President proposes to put in hardened silos in Wyoming.
The President's strongest ally on the missile, Sen. John G. Tower (R) of Texas, chairman of the Senate Armed Forces Committee, praised Reagan's ''courageous'' move but conceded he is only ''cautiously hopeful'' that the basing plan would work.
Critics also are cautious. House Speaker Thomas P. O'Neill Jr. (D) of Massachusetts scored the President for pushing unemployment to the back burner, but he did not attack the missile itself. ''I voted for it under Jimmy Carter, '' he said.
''There is a strong consensus to continue research and development'' on the missile, said Rep. Thomas S. Foley (D) of Washington. He said the majority of Congress favors an increase in military buildup, ''even in the harsh difficulties of a recession.''
Sen. Ernest F. Hollings (D) of South Carolina has blasted the MX plan as ''money down a rat hole,'' in the most searing attack so far. Citing a Pentagon adviser, he charged on an ABC-TV morning show Tuesday that the missiles could not be defended from nuclear attack.
But it is not clear that Senator Hollings will be able to gather enough allies to defeat the project. Many in Congress may be likely to follow the sentiments of House minority leader Robert H. Michel (R) of Illinois that ''technicians are more competent'' than lawmakers on whether the MX will work.
Congress will have its chance to act on the MX during the lame-duck session beginning next week, when it will take up defense spending bills, including about $2.4 billion earmarked for the missile in 1983. Most of that money is for reasearch, and the biggest fight is expected over $988 million slated for production.
All sides predict the battle will be close. But one plus for the administration: Now that the site is picked, congressmen who opposed the MX for fear it would go in their states may favor it. The Wyoming delegation is backing the President's plan.