ABBA is a Swedish pop group that attracts swarms on the streets of Paris and mobs in the pubs of London. But to the Washingtonians who milled around a smorgasbord yesterday, ABBA was about as familiar as the smoked reindeer on the table.

That didn't keep anybody away from a luncheon for the group at the Swedish Embassy. And afterward, lots of locals who normally listen to symphonies or the SALT debates promised to buy an album or two.

"I will improve myself," vowed Rep. Gillespie (Sonny) Montgomery (D-Miss.). "I will be a fan." Montgomery arrived late, but still in plenty of time for pictures with the maroon-haired Anni-Frid Lyngstad, who is one of the A's in ABBA.

The luncheon was another one of those rock-stars-meet-politicians-meet-record-company-executives affairs, plus some others thrown in for color and ballast.

In this case, the color was provided by Monica Lundegard, a Swedish textile artist who also had maroon hair and wore a maroon blouse festooned with perhaps two dozen pink quilted breasts. She stood near a large vase of red and pink roses, and the effect was, well, riveting.

"My friend gave this to me," she said of her blouse. "She said, 'Yes, you can have it, but you've got to wear it to the Swedish Embassy.'"

"Now don't ask if it's onions," said Lena Ulvenstam, a more traditionally attired artist standing nearby.

Guests at the luncheon included Sens. Charles Mathias (R-Md.) and Larry Pressler (R-SD.); White House social secretary Gretchen Posten, Livingston Biddle, chairman of the National Endowment for the Arts; J. Carter Brown, director of the National Gallery; Alejandro Orfila, secretary-general of the OAS; newscaster Roger Mudd, FBI Director William Webster; several socialites, and three-fourths of ABBA.

One member of the quartet, Agnetha Faltskog, was felled by a fever, which forced the group to cancel Thursday night's Washington concert.

Nonetheless, three of the four arrived late, as rock stars are supposed to, basked in applause, then headed for the smoked reindeer, herring, stuffed cabbage, Swedish meatballs and caviar at the giant buffet table. They've been touring the United States for a month now.

"America is a challenge," said Benny Anderson, who has that three-day-old-stubble look popular in men's magazines these days. "We don't have the same magnitude here as we do all over the rest of the world. It's sort of an ego thing, you know."

Anderson had lunch indoors, away from the cold rain on the terrace that forced Mrs. Sherman Cooper, for one, to arrange herself artistically in a dark print chair in the study.

As far ABBA, she confessed: "It's just my ignorance, but I've never heard of them."