After 40 years of engraving his image on Washington's art world, Franz Bader should know how to pack them into a show. Almost 1,000 people crowded into Bader's two-room I Street gallery and bookstore last night to celebrate his 80th birthday.

With his glowing dark eyes and bristling salt-and-pepper beard, the energetic Bader, who turns 80 on Monday, shuttled through the milling crowd, collecting bear hugs and birthday wishes and introducing artists and patrons.

After the reception, to which 5,000 had been invited, Bader and wife Virginia hosted a smaller dinner party, where he was presented with a birthday book filled with original art and photographs by "his artists."

"There are really not the words in my vocabulary to describe the vastness of it," said Mayor Marion Barry about Bader's contribution to Washington art. Barry had just been whisked through the gallery by Bader. "I wish I knew his longevity secret, so I could get some of it for myself," Barry said with a laugh.

Bader "is more than an individual," said longtime Washington artist Leon Berkowitz, who has known Bader for more than 30 years. "He's a whole episode. He was the only art dealer in the city in my younger years. He was what stood between us and starvation . . ."

Berkowitz's wife, Maureen, described by Berkowitz as "a budding artist in progress," noted that today is Berkowitz's birthday, making him a Virgo like Bader. "That means we're both persons of great stability and patience," Berkowitz joked.

"He has sold many of my paintings," said Swiss artist Brida Lazzarino, who has been represented by Bader for 11 years. "I thought at one time that he might arrange something for me in New York, but he's a little jealous of his artists. He likes to keep them here, for himself."

German artist Gunter Gumpert has been shown by Bader since 1965, as has Lee Weiss, who flew in from Madison, Wis., to surprise Bader at his party. "His gallery keeps him going," said Gumpert. "It's the only thing he is interested in so much--art and books. When I come here to Washington, there was nothing, there were three galleries. He did so much for abstract art here." Weiss said her watercolors of "remembered images" were influenced by long walks and talks with Bader along the C&O Canal.

Millie Bautista, executive director of the D.C. Commission on the Arts and Humanities, called Bader "a living arts institution" and read a lengthy proclamation from the mayor's office, specifying Monday as Franz Bader Day in the District.

"One thing I do want to tell you," said Bader, who came to this country as a refugee from Vienna and last night wore a tiny Austrian medal acknowledging his cultural achievements. "I love this city. It gave me the chance to start again a creative life, and make many friends, which is the creative secret of the world. And you see yourself how many friends. What else could you ask of life?"