On their own, David Crosby, Graham Nash and especially Stephen Stills have done little that is worth remembering. "It's mostly trash" was Still's succinct evaluation of his own solo work in a recent story in Rolling Stone - an opinion apparently shared by the record-buying public, which has made a point of avoiding his recent solo albums.

But together, Crosby, Stills and Nash, whose reunion tour has brought them to the Capital Center for two shows - one last night and another tonight - are something special. No matter that Neil Young isn't with them this time: The name CSN still carries a lot of weight in pop music circles.

Some of that is because the first CSN album, released eight years ago this month, had a lot to do with the subsequent rise of the singer-songwriter movement in the early '70s. Some of it is because CSN was the first of the rock "supergroups." And some of it is because the second album, recorded after Neil Young had joined the group, clearly inspired the formation of groups like the Eagles.

Last year at this time, though, the three of them weren't even on speaking terms. Crosby and Nash were performing as a duo, and when they came through Washington in late June, they were still seething from a SCNY recording session that aborted when Stills and Young erased their vocals and overdubbed some others.

"We found," said Nash then, "that we disagreed about what the music meant to us, about the depth and importance of what we were doing." Crosby, as usual, was more direct: "There were a couple of personal things that just didn't work out," he said.

But when Neil Young unexpectedly disappeared from the Stills-Young Band's Summer '79 tour, Stills was left high and dry. Soon after he turned up backstage at a show Crosby and Nash were giving in Los Angeles, and all was forgiven. He joined them for their encore, the old CSN favorite "Teach Your Children," and the reconciliation turned into plans to renew the partnership that had first blossomed at Woodstock.

So after six years and three tries, there's finally a new group album - and a tour to go with it. It's a chance for three rockers who are in their mid 30s and have been worn out by the business of rock 'n' roll to set aside their individual failures, to recapture past glories.

Public response thus far, however, has been lukewarm. The new CSN single, "Just a Song Before I Go," is No. 61 on the charts this week, and neither of the shows here in Washington is a sellout.

The sales of the album are likely to pick up once the CSN album is out in the stores and the tour a bit farther along - Washington is only the second stop on the month-long itinerary - but the lack of a full house is harder to explain. Three years ago, when Neil Young was still working with CSN, three Capital Centre shows sold out almost immediately.