Pro nuclear politics and disco roller-skating were booed equally last night by 20,000 rock fans who jammed into a sold-out Madison Square Garden for the first of five concerts by Musicians United for Safe Energy.

Specifically, last night the musicians were John Hall, Bonnie Raitt, Graham Nash, Jackson Browne, James Taylor, Carly Simon, Jessie Colin Young, Nicollette Larson and the Doobie Brothers all of whom played for free along with varying ensembles of the best studio musicians in the business.

On the surface it was like most rock concerts in gigantic sports palaces: a huge stage dwarfed by huge PA speakers, kids in blue jeans and T-shirts, holding up old sheets painted with the names of their favorite stars. The differences were in the lefty leaflets and a few people wandering around in white radiation fall-out suits and gas masks. And an anti-nuke film that was shown before the last act. And a few exhortations from performers on stage to attend a big anti-nuke rally on Sunday.

Otherwise it was rock 'n' roll, marijuana and howls of ecstasy, as usual.

There was no pretension of counter-cultural good vibes last night, yet -- however subtle -- the political implications of the event point to a force which some advocates hope will have the clout of the antiwar movement a decade ago.

Whatever rock and politics have in common -- and fanaticism and charisma immediately come to mind -- musicians here last night seemed to have created, for once, a unified effort. The bickering and ego-jostling that seem such an essential part of politics and rock 'n' roll were remarkably absent.

"Sometimes," said singer Graham Nash, "you have to look beyond all that and think about the real issues -- specifically evolutionary suicide."

And the rockers seemed to have done just that: focusing on an issue that one year ago -- pre-Three Mile Island -- probably would have failed to garner much public interest, or even to unite the rockers themselves.

The message of the evening was two-fold: Rock still has the power to draw massive segments of American youth (who in less than a month have shelled out about $1.5 million for 100,000 MUSE concert seats); and the issue of nuclear power may act as a catalyst for youthful political action in the coming election year. For every quaaluded boogie fan in the audience last night, there appeared to be scores of others resoundingly booing film clips of Jimmy Carter watching a Poseidon missile test and the Three Mile Island Cooling Towers, and cheering scenes of solar water heaters being installed.

Booed along with the mushroom clouds was Bonnie Raitt's announcement of a Saturday solar roller disco.

Echoling the sentiments of many here, 19-year-old Joyce Brown from Queen's said: "I really came here to see Jackson Browne. But then I started thinking about all this nuclear stuff, and it scares me."

"Any politician who goes into the Pennsylvania primary next year," said MUSE staff consultant Sam Lovejoy, "and says anything pro-nuke is going to find himself in big trouble."

Maybe the kids -- the audience here is largely young, 18 to 23, -- are beginning to sense that. And maybe the politicians are, too. One staffer reported Jerry Brown's office has been Calling MUSE headquarters every day for the past month, "sniffing around for an invitation to speak."

None was forthcoming because the organization has chosen to remain decidely non-partisan.

But, when the anticipated $600,000 from the concert receipts, and projected $2 million for record and movie rights are divided up, a substantial number of anti-nuke programs will be bankrolled. The political consequences could be strong.