About two dozen young demonstrators protesting the U.S. presence in El Salvador paraded in front of the Concert-Gebouw here tonight before the start of the National Symphony Orchestra's concert and later staged a noisy protest inside. There were no injuries and no arrests.

The demonstration in front of the concert hall delayed the start of the 8:15 concert, attended by Queen Beatrix, by five minutes. Patrons using the main entrance had to step over the bodies of young people stretched out full-length, face down, on the steps in front of each of the doors. Other young people carried banners reading, "U.S. Walks Over Corpses in Central America." In the street, demonstrators with lighted torches passed out leaflets that said "USA: The Shrine of Hypocracy" (sic).

Conductor Mstislav Rostropovich opened the concert with the Dutch national anthem and "The Star-Spangled Banner," on a stage decorated with a large emblem reading "1782-1982 Dutch-American Friendship."

At 8:33, after the opening overture by Samuel Barber, protesters ran up the aisles shouting slogans and showering leaflets on the audience and some of the orchestra. Rostropovich, who was just reentering the stage, stopped and stood quietly until the demonstrators left. No police intervened at any point. An Amsterdam resident said, "Well, we are a free country, too, and these people demonstrate at the drop of a hat."

The demonstration was put on by the Amsterdam Committees for El Salvador, Guatemala and Nicaragua, which are holding a joint rally here on Feb. 27. One of their leaflets was headed, "Congratulations Reagan on Your Program of Human Rights in El Salvador," and showed a photo-montage of corpses in the streets of El Salvador.

After the disturbance, the concert proceeded without interruption.