Martina Navratilova, the best imported-domestic tennis player on the women's tour last year, was out late Monday night sipping French champagne and celebrating her 6-2, 6-1 trouncing of Tracy Austin.

"It wasn't Piper Heidsieck," said Peachy Kellmeyer, assistant executive director of the Women's Tennis Association, who was buying. "We can't afford it."

Navratilova can. She won $90,000 for five days work at the Colgate Series Championships, $75,000 for the singles title and $15,000 for the doubles championship (teaming with Billie Jean King). She might as well get used to Washington's watering holes. It looks like the tournament, held here for the first time this year, will be back in 1981.

Although a decision will not be made for several months, officials of the Colgate Series and the Colgate-Palmolive Co., interviewed Monday night, said they expect the tournament, one of the four most important in women's tennis, to return to Capital Centre next year.

Edy McGoldrick, executive director of the Colgate International Series, said, "I think there's an extremely good chance (of coming back). We've been very pleased. I think the arena facilities are very good and we've gotten very good press coverage in Washington and nationally. I would like to see us come back."

John E. Grimm III, vice president of Colgate's Sports and Recreation Division, said, "I think all things being equal, one is better off staying in one place and trying to build it, building an entity as we have at the Garden (Colgate is sponsoring its last Grand Prix tournament for the men -- the Masters -- this week at New York's Madison Square Garden). And Washington being the capital of the country, there is a prestige factor in having the series championship here."

Last year, the tournament was played outdoors in Palm Springs, in the middle of a California desert. The tournament was not a mirage but it did tend to get lost. The decision to come east and in out of the cold was made in hopes of raising attendance and media consciousness. (McGoldrick is proposing a post-Christmas tuneup tournament next year to build interest further and help players get over the holiday blahs.)

"Tennis is heading indoors," said Chris Evert Lloyd, who came in third after two first-place finishes. "I think they feel they can get bigger crowds and control the conditions. We got nearly 10,000 (9,200) for the finals indoors on Monday and we would have gotten 3,500 outside."

Although more than 50,000 tickets were sold for the five days, there were some 4,400 no-shows Friday when Snowy weather intervened and Evonne Goolagong Cawley defaulted becuase of injury.

"Overall, we're very pleased with the results," said Ray Benton, the tournament director. "We started out very strong: we had nearly 7,000 the first night and jumped to 9,000 the second. We had sold 9,000 tickets for Saturday but the weather hurt us. I was exceptionally pleased with the number who came out on Sunday."

The tournament drew its largest crowd, 9,800, on Sunday, a makeup for the canceled Saturday matches, on the day of the NFL playoffs. Benton predicts the tournament "will sell out, 15,000 seats for next year's semis and finals."

The players had few complaints about the tournament. Navratilova and Evert Lloyd did not even complain about having to get up early to attend a conference announcing that they and Austin had accepted invitations to the $200,000 Clairol Crown, a tourney for the top four players that will be played in March. Both would have liked to see the Colgate Series Championship, which was billed as the one that would determine the No. 1 player in women's tennis for 1979, played in 1979. Evert Lloyd would have liked more than an hour a day practice time on the court, which was faster than she liked. Navratilova, however, liked it just fine.

"It was fantastic," said Navratilova. "I had five, not even bad, bounces, inconsistent bounces the whole time. I didn't miss one shot the whole week because of the lights."

Navratilova was surprised but not disconcerted by the number of lopsided matches (only one match was not won in straight sets). "If you have Borg, Connors and McEnroe in a tournament, I'll bet any money they'll all be in the semis," she said. "There's the top three and then a dropoff. It's the same with the women now, too." CAPTION: Picture, Martina Navratilova, Chris Evert Lloyd and Tracy Austin attend press conference announcing their participation in $200,000 invitational tennis tourney in Carlsbad, Calif., in March. AP