While hundreds of voices sang happy birthday, Jacob Kainen, dean of Washington artists, stood surrounded by his paintings and his friends in a pillared hall of the National Collection of Fine Arts Thursday night.

Kainen's host and longtime friend, NCFA director Joshua Taylor, presented a cake with one candle representing 70 years, and everyone cheered as he blew it out. Many were also cheering the fact that three celebratory exhibitions -- here, at Lunn Gallery and at the Phillips -- have revealed Kainen's newest work to be the best he's ever done.

"It's the happiest day of my life since my wedding," said Ruth Kainen, who married the artist in the early 1970s, and has played no small part in getting his art out where people can see it.

For though Kainen has been a nucleating force in the art world here since he arrived from New York in 1942, he had been known chiefly as the Smithsonian's curator of graphic arts. It was only in 1976 that an NCFA retrospective of his prints revealed his vast graphic output to the public.

His paintings, however, though closest to his heart, have not been seen in a survey show here since 1945.

Kainen's new retrospective, entitled "Jacob Kainen, Five Decades as a Painter," is small -- only 19 works, but it outlines the development of his style from realism to abstraction to figuration and back to abstraction.

"In the '30," Kainen explained, "those early scene, like "Tenement Fire," weren't 'realist' but 'expressionist' works, and expressionism was a low current. I was close to a group called The 10 -- Rothko, Gottlieb, De Kooning -- but unlike them I always had a feeling for shape. Those trees, for example [he made a brushstroke in the air] they're shapes, not trees -- cyptic symbols, which is, after all, what artists make."

He moved on past "M Street," marking Kainen's arrival here in the '40s, when he painted only at night and on weekends. As the paintings became more and more abstract, he explained, "you can see I'm getting more emotional, expressionistic, rhythmic, distorting more." His hands flew and his voice rose with excitement.

He stopped talking in front of a particularly tormented work from 1954 called "The Vulnerable." "Of course artists shouldn't know or talk too much about what they're doing. After all they're operating in the realm of sensibility and emotional turmoil . . . In the '50s I despaired about society.

"But I was never a true abstract expressionist," he said, "though I was both abstract and an expressionist. I was always interested in forms, in patterns. I didn't want just emotional brushwork. By the late '50s abstract expressionism was everywhere -- society ladies were doing it, and they were teaching it in the schools, telling students it wasn't necessary to learn to draw -- just express yourself. Others were staining canvas, which I didn't want to do -- it gave a nice, fresh watercolor feeling, but lost the mass, the palpability of paint.

"So I went back to the figure -- out of style again, of course." He pointed to a loosely brushed portrait of artist Gene Davis, typical of these paintings from the '60s.

When realism came back, Kainen began to do abstractions again -- "not just because others had turned against them, but because I wanted to. But I didn't want to do just handsome abstractions, so I began to work again with signs and symbols, but in a painterly way. Because the handling of the pigment is still what differentiates a real painter. It has to be crisp, fresh and alive." His hand swept the air once again with his imaginary brush.

"Now I'm summing up," he concluded, standing before his most recent work, "Constantine II," a minimal form pulsing with splendid color and brushwork. "I'm trying to eliminate everything that's not essential to either feeling or design."

Here and in the magical, tenderly colored news monotypes at Lunn Gallery, he had done just that. His shows continue through Jan. 5.