Generally a concert by Gordon Lightfoot is not unlike a ride down the "Carefree Highway" he made famous. The trip is smooth, the sights are familiar, the pace leisurely. Last night at Wolf Trap, however, the ride was bumpier than usual.

It was the Canadian troubadour's first performance in months, and the layoff was perhaps responsible for a bothersome problem that developed early in the show. His quintet's accompaniment, through only slightly amplified, frequently overshadowed Lightfoot's woodsy baritone. Consequently he was at his best working in an essentially acoustic format, performing the seven-minute saga, "The Wreck of the Edmund Fitzgerald"; his early hit, "The Last Time"; and the lovely "Minstrel of the Dawn." Later, Lghtfoot confessed to being a little rusty on some of the songs. His sloppy attempt at a rock 'n' roll tune was an outright disaster. "This is what's called saving yourself after laying an egg," he said good-naturedly as he put htat song behind him and moved on the lilting "If You Could Read My Mind."

The second hour-long set was a vast improvement over the first. It was as if the rehearsal was over and Lightfoot was at long last ready to do justice to his impressive list of ballads, including "Sundown" and "Race Among the Ruins."