Last night's concert at Lisner Auditorium was as much a social as a musical event: a gathering of a clan and a celebration of growing strength and pride. As such events usually do, it ran somewhat longer than a standard concert; congratulatory telegrams were read from absent members of Congress; distinguished members of the audience were applauded. And Mayor Marion Barry was present in person to read his proclamation of Sept. 6 as Gay Chorus Day in Washington and to accept a long, loud ovation.

After three hours, the overburdened air-conditioning system almost gave up, unable to cope with the standing-room audience, the heat and humidity. And it is doubtful that anyone in the audience could have enjoyed equally all of the music presented by the three gay men's choruses of Seattle, Los Angeles and the District, with a half-dozen smaller subgroups.

The repertoire ranged from the solemn--a Gregorian "Jubilate Deo," a Bruckner cantata and two of Poulenc's exquisite "Laudes de S. Antoine de Padoue"--to the trivial, "Johnny One-Note," "Over the Rainbow" (twice!) and a medley of television theme music.

But there were no complaints about longueur or unevenness, and when the curtain came down for the last time at 11:30, the audience was applauding as though it could take several more days of similar material. This will be available, in fact, tonight through Sunday, when the three choruses who sang here join nine others in New York for a four-day gay choral festival titled "Come Out and Sing Together!" which will include the world premiere of a new piece by Ned Rorem.

Two of the choruses last night reflected to some degree the cities of their origin. The Gay Men's Chorus of Los Angeles, directed by Jerry Carlson, did some serious singing but excelled most clearly in entertainment--particularly in comedy.

The Gay Men's Chorus of Washington, D.C., directed by James Richardson, was sometimes quite entertaining but seemed most impressive in the exercise of power. It used effectively the richest-sounding bass section of the three groups and engaged in some thinly veiled manifesto-mongering with Jean Berger's powerful "Hope for Tomorrow," a very moving setting of a text by Martin Luther King Jr. The D.C. group, the newest of the three, has progressed significantly since its establishment two years ago.

The Seattle Men's Chorus was the most purely musical of the three groups, singing more advanced repertoire with beautifully blended tone, exquisitely precise diction and subtly calculated dynamic nuances. And at the end, when each conductor in turn took the massed voices of all three choruses for a single number, the Seattle music director, Dennis Coleman, made the nearly 300 voices under his direction sound like the Seattle chorus.