How much Brahms does a person need? On Wednesday night, which marked the composer's 153rd birthday, visitors to the German Embassy were offered some five hours of his chamber and vocal music, presented by the Washington Music Ensemble in the kind of informal atmosphere best suited to that kind of music.

"You are invited to arrive and depart at your pleasure," said the tickets. When the program began, shortly after 7, the embassy's small auditorium was filled nearly to capacity. When it ended, just before 12:30, there were about two dozen, some of whom had been there from the beginning. Others came late or left early after absorbing as much Brahms as suited their needs.

The music, like the refreshments, was served buffet-style. It came in five segments, each combining vocal and instrumental music except for the middle one, which offered the monumental (at least in length) "Magelone" songs, performed by baritone Jerome Barry. The food varied through the evening, beginning with standard meats and salads and later modulating into fruits, Viennese pastries and coffee at the end.

Not many patrons consumed all the music, but the food vanished by the end of the evening. At its height, the celebration had divided into two parts, some people nibbling and chatting in the foyer while others listened to the music in the adjoining auditorium. Passage from one party to the other was easy and spontaneous, and the availability of both created an excellent ambiance for enjoyment.

During a program of such length, the quality of the music was naturally variable but generally good. The musician who gave consistently the finest performances was one who never took a solo role: pianist Alan Mandel, who performed in chamber music and as accompanist for Barry and soprano Elizabeth Kirkpatrick.

Perhaps the finest music of the evening was the Op. 8 Trio, in which Mandel was joined by violinist Mary Findley and cellist David Premo. The two Op. 120 sonatas, published both for viola and for clarinet, were heard on both instruments. In No. 2, clarinetist Charles Stier gave a smooth, idiomatic performance that was not matched by pianist Maribeth Gowen. In No. 1, she was a better match for violist David Basch.

Kirkpatrick and Barry both sang with the intelligence and fine sense of style that have long been familiar to Washington audiences, but both had fairly serious problems controlling pitch and tone in their upper registers.