The National Symphony Orchestra opened its 60th season last night with a surprise. Drinks on the house. Thousands of them.

After an evening of Mussorgsky, Copland and Schuman, and a standing ovation for the players and conductor Mstislav Rostropovich, most of the near-capacity audience stood sipping wine on the River Terrace outside the Kennedy Center Concert Hall. concert.

Albert J. Beveridge III, the NSO's president, had issued an unprecedented general invitation from the stage at the end of intermission: "The board, the orchestra and the management invite you to join us on the River Terrace for refreshments to toast the new season." Later, he was circulating on the Terrace, introducing himself to patrons, thanking them for coming and inviting them to come again.

The refreshments turned out to be mostly white wine, set out on a table and constantly replenished by waiters, but those who preferred could go to other tables for soda water or soft drinks. "This is the first time they've done anything like this," said one veteran NSO subscriber. "I think I like it."

One good point, several fans noted, was that they could stand around talking about the music instead of making a mad dash for the parking spaces to avoid bottlenecks complicated by repairs underway in the garage.

"We looked into the costs and found that it would be less expensive to serve free drinks for everyone downstairs than to hire a caterer and set up refreshments for invited guests in the atrium," an orchestra staff member said. Even the patrons who didn't go out to the terrace were offered drinks by waiters with trays circulating in the Grand Foyer.

There was no security in effect; the National Symphony could have been entertaining people who had wandered in off the street, though there usually aren't many of those at 10:30 p.m. in the Kennedy Center, or giving drinks to people who had gone to some other performance. But "The Playboy of the Western World" had let out earlier and "Shogun" was still going on despite continuing efforts to shorten it.

The concert was worth a special celebration, musically and in terms of special events. It was highlighted by works of two major American composers celebrating important birthdays this year; a musical memento of cellist-conductor Hans Kindler, the NSO's founder; and a rousing performance of a perennial favorite: Mussorgsky's "Pictures at an Exhibition" as orchestrated by Maurice Ravel. The orchestra also welcomed five new members, as well as one player who will be participating under a special program and three members who had been promoted to section leaders.

The program contained no symphonies, but the combination of an overture, a ballet suite and three arrangements from the music of Mussorgsky worked quite well, largely on the principle of contrast.

The bright, brash, vigorous "American Festival" Overture of William Schuman (who was 80 last month) contrasted effectively with a gently lyric, luminous performance of the "Appalachian Spring" Suite of Aaron Copland (who will be 90 in November). The Copland work, subtly accented, light in texture and flowing with a special grace, was one of the most beautiful performances Rostropovich has conducted here in recent memory. Its effect was enhanced by its juxtaposition with the vigorous rhythms and bright instrumental colors of the Schuman overture.

After these two American classics, Hans Kindler's Mussorgsky arrangements seemed pleasant enough but relatively undistinguished. They were "A Tear," arranged from a short piano piece, and the love music from Act 3 of "Boris Godunov," with the vocal parts given to instruments. Kindler's competent but unadventurous orchestration of Mussorgsky was followed by Ravel's virtuoso arrangement, one of the most imaginative pieces of orchestration in classical music, and it suffered somewhat from the inevitable comparison.

In the Mussorgsky, Rostropovich was clearly determined to show what his orchestra can do in his 14th year as its music director, and there was no question that it has grown enormously in that time. The music's emotional and pictorial variety was well presented, the ensemble sound was precisely coordinated and well balanced, and the players were splendidly responsive to his baton. The phrasing and accents had a subtlety that they did not have in his first years, and his control of dynamics was most impressive -- not only in the crescendo and decrescendo of the "Bydlo" episode, which shows an ox cart lumbering by, but in the carefully calibrated restraint with which he led up to the resounding climax at the end.

After intermission, appropriately in a program that featured two American composers, Rostropovich received Columbia University's Ditson Conductor's Award for his "vital role in the creation, performance and recording of new works by American composers" and his "deep commitment to American music."

The new members, playing with the orchestra for the first time, were flutist Carol Bean; violist Yun-Jie Liu; second violinist Pavel Pekarsky, whose father, Lev, is also in the second violin section; contrabassist Dennis Roy; oboist William Wielgus; and contrabassist T. Alan Stewart, who has been given a one-year contract under the Music Assistance Fund, which encourages talented African American musicians to pursue careers in American symphony orchestras. New players in principal chairs are violist Roberto Diaz, second violinist Charles Wetherbee and assistant principal second violinist Paul Roby.