In 1978, just when he was on the brink of superstardom, Jackson Browne put his commercial career aside to work for the anti-nuclear movement. Last night at Merriweather Post Pavilion, he was back at his old job. His two years of political leadership didn't make him a speechmaker but did transform him into a self-assured singer and a rabble-rousing rock 'n' roller.

Browne used to sing songs like "Rock Me on the Water" and "Here Come Those Tears Again" with an introspective romanticism, as if he had just glimpsed the apocalypse. Last night he sang the same songs with the assertive confidence of one who has stared down such visions and can now offer some counsel to those getting their first look. The old songs carried new connotations; the new songs made his acquired toughness explicit.

The music behind the vocals also benefited from this new maturity. Browne gave his all-star band longer and freer solos. On Browne's moving eulogy to Lowell George, "Of Missing Persons," a swelling organ moan was added by Bill Payne, George's colleague in Little Feat. Russ Kunkel broke up songs and recharged them with the deepest sounding drum rolls. But the real star of the show was David Lindley, who played like one of rock 'n' roll's greatest guitarists. Lindley's fiddle and lap-guitar solos were so eloquent they seemed to extend Browne's lyrics into a new language.

The only politicizing was a wordless slide show of nuclear reactors, demonstrators and children during "Before the Deludge." The most forceful statement, though, was the hard-hitting rock 'n' roll beat that gave Browne's music an energy it lacked before.

Jackson Browne's three-hour, 23-song show will be repeated at the Pavilion tonight and tomorrow night.