There's nothing like a clear and present danger to make a party come alive, and if there's one thing they agreed on at the party at the Center for Defense Information on Capitol Hill last night, it's that the MX missile plan is just that.

"A $100-billion monstrosity," said Rep. Ron Dellums (D-Calif.).

"An absolute boondoggle," said ex-senator Eugene McCarthy.

"I'm not optimistic about it," said philanthropist Stewart Mott, "but I'm not optimistic about anything in this administration."

That was just the start of it at the kickoff party six House members hosted for the National Campaign to Stop the MX, a coalition of about 30 groups -- including the Taxpayers Union, Friends of the Earth and SANE (the National Committee for Sane Nuclear Policy) -- that has just moved to Washington to convince a largely disbelieving Congress and an unsuspecting nation that the MX must be stopped.

So far, nobody even agrees on what the MX will cost.The Air Force says $33 billion. Critics say more -- as much as $100 billion.

One of the leaders of the flight is Utah State Sen. Frances Farley, many of whose constituents are displeased at what the MX, the Air Force's land-based nuclear missile system, could do to their state and neighboring Nevada where it would be located. "The plans call for tearing up a portion of western land the size of Pennsylvania," said Farley, who is in town to lobby the Utah and Nevada congressional delegations.

"But it's not just environmentalists and Utah," said Chad Dobson, who will be heading up the Campaign's Washington office. "In a few years it's likely that the Russians will develop the technology to detect those missiles underground. Then the whole system is obsolete."

"The system is dangerous, unnecessary, impractical and expensive," said Dellums. "Not one member of Congress can even tell you how much it's going to cost. They can't even tell you about the basing mode. There are 30 different designs. We don't even know if we have enough cement to build all the tracks."

Dellums, a longtime congressional opponent of the MX, was one of the sponsors of the Campaign's maiden pow-wow. Guests munched on Brie and crackers, sipped white wine from big glasses, and watched, between earnest conversations, a double feature being shown on a video machine: an Air Force film explaining the MX and a three minute Soviet cartoon, courtesy of the Soviet Embassy, called "The Balance of Fear."

"Watch this," said one of the guests as the Air Force film went on. There were a few sighs as the show continued. "The greatest threat to the MX is exposure," Dellums was saying in the hall. "Once the American people find out about it, that will be that."

Present plans for the MX call for 200 missiles, 4,600 silos to house them and miles and miles of underground track in Utah and Nevada to shuttle the missiles around on, thus keeping the Soviet Union from figuring out where they are. "It's like a carnival shell game," said Rep. Paul Simon (D-Ill.).

"Did you see the cartoon?" said Farley. "Brezhnev is standing before a table with three walnuts. The cartoon says, 'Which one is hiding the missile?' And Brezhnev picks up a hammer and smashed all three." Nobody thought that was very funny.