''He could take something and turn it into a fully scored, well-thought-out, harmonically structured masterpiece in about a minute and a half,'' Mr. Barlow said in an interview yesterday. ''Brent could pick his way through anything immediately, which meant he had the special requirement it was going to take to walk into the Dead overnight. He was musically central to the band, but he was so good at what he did that he was able to become fundamental to everything that the band was doing musically without it being immediately apparent to the audience.''

Mr. Mydland was born Oct. 21, 1952, in Munich, West Germany, to an American military family and grew up in Concord, Calif. He worked with the group Batdorf and Rodney in the early 1970's, then joined a Los Angeles-based band called Silver. Bob Weir, the Grateful Dead's rhythm guitarist, hired Mr. Mydland in 1978 to tour with the Bob Weir Band and its successor, Bobby and the Midnites. He appears on the Midnites' self-titled album, and joined the Grateful Dead when Mr. Godchaux left the band in 1979. Mr. Godchaux died in an auto crash in 1980.

His Songs on Albums

Mr. Mydland appeared on the band's 1980 album ''Go to Heaven,'' which includes two of his songs, ''Far From Me'' and ''Easy to Love You.'' He also performed on the band's two live albums recorded in 1980, ''Dead Set'' and ''Reckoning.'' The Grateful Dead did not make another album until 1987's ''In the Dark,'' for which Mr. Mydland's keyboard parts helped carry the song ''Touch of Gray'' into the Top 10.

The band's most recent album, ''Built to Last,'' included Mr. Mydland's ''We Can Run,'' an ecological song that was made into a video for the Audubon Society, and ''Just a Little Light.''

The Grateful Dead, which was founded in 1965, completed a short tour on Monday. The band's next scheduled performance was to take place Aug. 31 at Shoreline Amphitheater in Palo Alto, Calif.