Virginia Gov. Charles S. Robb, Mount Vernon High School Class of '57, returned to his alma mater last night to address the 439 members of the latest graduating class and reminisce about the way things were.

"I am a product. . . of the Eisenhower years," Robb told the enthusiastic crowd of parents and students assembled in the darkened auditorium. "Younger than your parents, older than Camelot. In the spring of 1957, drug stores still had soda fountains, color television was an expensive experiment, and the Washington Senators were right where they belonged--in Washington, and last in the American League.

"And Ronald Reagan," the governor said with a grin, "had made the first of his successful transitions, from movies" to selling soap on TV.

For the clearly delighted Robb, who played varsity basketball and practiced student politics during his two years at Mount Vernon, the commencement was a return to friendly territory. Mount Vernon students elected Robb governor in a mock contest last year by a 7-to-3 margin, and the Mount Vernon Marching Majors Band faithfully tootled at his inauguration.

Last night the governor said: "I have looked forward to this evening a long time. I declined all other high school invitations in the Commonwealth except this one. . . My only point in telling you at this time is to let you know how terribly proud of Mount Vernon High School I am."

More than one Mount Vernon fan described the governor's visit as a much needed boost for a school that this year suffered the humiliation of having its basketball team suspended after its athletic staff was accused of improperly recruiting athletes. "He's pulled us up tonight," history teacher Timothy Kerlin said after the speech.

Robb, who was accompanied by his wife, Lynda, took time to praise the teachers' calling, describing it as "the most difficult and demanding of all modern professions."

Difficult perhaps, but apparently not because of students like Robb. None of the veteran teachers present who had taught or coached the future governor 25 years ago could remember him as anything other than a "nice fellow to have around."

"The only trouble I can remember him getting into was throwing the basketball in the hallway once with some of the boys after practice. They broke a globe, he confessed to it and I gave him a few days' detention," retired principal Melvin B. Landes recalled.

"He had a smooth, courteous personality," Landes recalled. "I never imagined he'd be governor, but, come to think of it, he did have a lot of dignity for a fellow that age."

Robb was not the only celebrity who was to address Northern Virginia high school graduates last night. Others included former Republican Gov. John N. Dalton who was to show up at W. T. Woodson High in Fairfax, Sen. Strom Thurmond (R-S.C.) at McLean High and television journalist Sam Donaldson at Herndon High.