The pre-concert rituals governing the trip down the aisle to your seat (people-watching and friend-greeting) and the mid-concert rituals governing intermissions (a certain amount of drinking and a lot of smoking) were interrupted last night by the patter of little feet and the thud of slightly larger ones.

The occasion was the first of a series of family concerts given by the National Symphony at the Kennedy Center. Tickets were free and by 6:45 a large crowd had already accumulated in a sort of lumpy line.

This time some of those who tripped down the aisle wore Cub Scout uniforms. Most held tight to a hand or two, and seats that looked unoccupied at first glance tended to contain at least one small member of the audience scrunched down comfortably.

Intermission talk revolved about the relative merits of chocolate-covered raisins and mints and how late bed time would be.

The concert marked the National Symphony debut of Hugh Wolff, who is this year's Exxon Arts Conductor. A graduate of Whitman High School, Wolff has packed a lot of experience into a very few years: study in Paris and at Peabody Conservatory, awards for piano performance, and conducting tours.

On the podium he gives an impression of precision and assurance. Last night, there was more tenseness than tension in his beat, which the orchestra reflected in some brittle rhythms, but in general they played nicely for him and he drew well-balanced and clean sonorities from each section.

The program was calculated to please everyone. For the youngsters, there was Ives' "Variations on America," Adel Sanchez's marvelous trumpet solos in the stratosphere of the Bach Second Brandenburg Concerto, and the swinging trombone fugue of the scherzo of the Hindemith "Symphonic Metamorphoses."

The more experienced contingent had, in addition, the finale of the Beethoven Third Symphony and the Rachmaninoff "Rhapsody on a Theme of Paganini" to enjoy.

Pianist Eric Himy, the 1979 winner of NSO's young-soloist competition, was the soloist in the Rachmaninov and used this romantic effusion to display an awesome technique and impressive musicianship.

Wolff, in true Bernstein-young-people's-concert form, introduced each pieve with snatches of themes and a smattering of analysis.