The Rev. F.C. Barnes and the Rev. Janice Brown, the North Carolina duo that has returned old-fashioned, unvarnished southern gospel to the top of the gospel charts, were scheduled to close the gospel festival at the Fort Dupont Summer Theater last night, but they never showed up. There was no explanation to the crowd from the stage when the concert suddenly ended, and National Park Service stage manager Howard Banks later said that the promoters had not received any word from the duo.

Nonetheless, the festival offered up 3 1/2 hours of the best of local gospel music to the crowd spread out over the grassy field. Among the highlights were Gloria Hightower, who delivered her spiritual message with the earthy style of rhythm and blues, and the 55-member Donald Vails' Salvation Corporation, which belted out its call-and-response arrangements in oceanic waves of sound.

The evening's biggest revelation, though, was 11-year-old Robin (Sugar) Williams of Anacostia, who not only possessed an enormous voice, but used it with a stage presence and inflections of someone three times her age. When she sang "Amazing Grace" to Vails' piano accompaniment, she pumped up the old standard with gravelly growls, dramatic whispers and whooping hollers.