MIKHAIL BARYSHNIKON has lowered the boom on the gossipmongers. For the first time since his appointment in June 1979 as the new artistic director of American Ballet Theatre, the great Russian dancer, who took office last month, has begun to unburden himself in detail about his plans and hopes for the company what Baryshnikov is now doing and proposing and what the increasingly promiscuous rumor mill of the ballet world hs been saying he would do.

Baryshnikov's intentions are particularly pertinent to Washington right now, since it is here during ABT's four-week engagement at the Kennedy Center starting Dec. 10 that the company will make its first appearances anywhere under his stewardship -- the New York season won't begin until next April, following a 10-city tour. It is this city, then, that the first effects of Baryshnikov's supervision will become visible.

Let it be known first off that Baryshnikov himself will be dancing with the company, and in fact will take to the stage here in Washington -- for the first time as an ABT dancer since he left the troupe in 1978 to join the New York City Ballet. Despite heavy administrative burdens, he smiled with that boyish twinkle of old and said, "Of course I'll be dancing -- I'll be in the third row back!" The actuality is that he'll be dancing here in his customary leading roles in "Giselle" (partnering Gelsey Kirkland), "Push Comes to Shove," his own version of Tchaikovsky's "The Nutcracker," and for the first time with ABT, George Balanchine's "Prodigal Son."

When Baryshnikov defected to the West in 1974 at the age of 26, he was immediately everyone's darling; nobody had any but kind words to say about him, as an artist and as a person. As his fame and power in the precarious, jealousy-prone ballet universe increased, so did the grumblings in the gossip circuit.

Of late, there has been all manner of wild prognostications about what his assumption of ABT's reins would mean: for example, that he was going to dismantle the company's heritage of American choreography, and replace it with stale Russian warhorses; that he would fire most of the dancers and install an unnamed bunch of Russian cronies; that he would sever all ties with his predecessors, former co-directors Lucia Chase and Oliver Smith, as well as their longtime collegues; that he would do nothing to foster new, original repetory for the troupe; and that he would close up the company's ballet school for good.

But in each instance, Baryshnikov's actions and statements have contradicted what was "predicted."

The company has reengaged Patrick Bissell, Fernando Bujones, Alexander Godunov, Cynthia Gregory, Gelsey Kirkland, Kevin McKenzie, Marianna Tcherkassky and Martine van Hamel as principal dancers for the season. Though no contracts have been signed at this date with Natalia Makarova and Anthony Dowell, negotiations are in progress and optimism rides high for a successful resolution. Magali Messac, formerly with Pennsylvania Ballet, will come aboard as a new principal, and Johann Renvall and Lisa de Ribere have been promoted to soloist rank. The only broadly familiar names missing from the lineup will be Kirk Peterson, John Meehan and George de la Pena; of these cases, only Peterson's seems to have involved friction with the new management.

"We have some very fine new dancers too," Baryshnikov said recently in New York. "For instance, there's Ronald Perry, who was with Arthur Mitchell's Dance Theatre of Harlem. He's a wonderful dancer with easily the potential, I would say, to become a principal. He'll do 'Fancy Free,' 'Theme and Variations' and some Tetley this season, and we expect he'll become very important to the company. Dominique Khalfouni, who has left the Paris Opera Ballet, will dance with us a few times. We hope to show her in the romantic repertoire in which she's so excellent.

"Otherwise, I don't think we'll be having 'guest artists' this year. I'd like to create an atmosphere in which there can be an even closer relationship between the experienced dancers and the younger ones -- to hold on to the tradition of one generation passing on wisdom to another which has been one of ABT's main strengths. This company has such wonderful dancers, and they're as good as they are because they have 40 years of development behind them."

Baryshnikov shows no inclination towards a radical break with the ABT past. There's evidence of this in his continuing working associations with "the old guard." Anthony Tudor remains as "choreographer emeritus," Nora Kaye continues as associate director, and Oliver Smith has been appointed to serve as co-director -- along with Baryshnikov and Richard Englund (director of ABT's "second" unit, the touring Ballet Repertory Company) -- of a new, Rockerfeller Foundation-funded progam for emerging choreographers.

"Yes, I have extensive plans for the future, some things that may surprise everyone," Baryshinikov said. "I want to set idealistic objectives, but I realize that it will take time to get there, and along the way there will have to be compromises to stay within our means. But I do not want to change the face of the company -- the company is what Miss Chase and Oliver Smith have so successfully created these many years, the repetory combining tradition and the new, and the superb dancers. I just want to go further in this direction. We are disucssing possible commissions, both for ballets and music. We want to build the new choreogrpahy workshop with the company, with an exchange of dancers and ballets. We want to maintain the American repertory and extend it -- we will do Paul Taylor's 'Airs' this season, for example. And I think it's most important in coming seasons to have leading choreographers continue to contribute new work to the company, people like Kenneth MacMillan, and younger ones like Jiri Kylian and Choo San Goh." k

Another high priority for Baryshnikov is the cultivation and refurbishing of classics, both modern and historical. Programs at Kennedy Center, for instance, will include the ABT premiere of Sir Frederick Ashton's "Les Rendezvous"; Baryshnikov's restaging of Act III of "Raymonda"; the Washington premiere of Natalia Makarova's full-length revival of "La Bayadere"; plus such repertoire staples as "Les Sylphides," "Interplay," "Rodeo," "The Moor's Pavane" and "Theme and Variations."

In addition to Ashton's "Les Rendezvous," which dates from 1933 ("the ballet is to technically brilliant the cast can dance its legs off," Baryshnikov says), Balanchine's "La Sonnambula," Nijinsky's "Afternoon of a Faun," MacMillan's "Concerto" and some Bournonville pieces will enter ABT repertory later this season, though not in Washington. And besides the "Raymonda" excerpt, Baryshnikov himself will stage dances from "Le Corsaire" and "The Sleeping Beauty," Act III, to make up an evening of Petipa divertissements.

Baryshnikov will also begin to spruce up the company's productions of "Giselle" and "Swan Lake," this season, preparatory to full-scale reworkings further down the road. "It'll be mainly a healing process," he says, "particularly in regard to the mime and stylistic details in 'Giselle' and the character dancing in 'Swan Lake.' The Wilis in Act II, 'Giselle,' for example, shouldn't be such dead creatures -- they must be frightening, yes, but also very seductive." Eventually but "for sure," he adds, the company will have a new production of "Swan Lake," for which he hopes to persuade Franco Zefirelli to create the designs -- "he's never done a ballet production, and he's wanted to all his life," Baryshnikov says.

As for the ABT company school, it is true that its operation has been very largely curtailed, cut back for the present, in fact, to a scholarship program for some 20 students under the directorship of Patricia Wilde. The change was necessitated, in part, by the company's loss of studio space in its recent, forced move of headquarters from midtown to lower Manhattan. But Baryshnikov also felt the school wasn't organized along strict enough lines, and he wants gradually to develop it anew "when we have the money, the teachers, the space and the time," more or less on the model of Balanchine's School of American Ballet. "ABT needs and deserves a fine school," he says.

Does he worry about the drain on his energies having both to direct a company and be a dancer will entail? "Sure, it's a problem," he says, "but I hope to be able to pace myself, to keep myself within a discipline to do both things simultaneously. I know it's not going to be easy. As far as directing the company is concerned, I have different moods. I'm very depressed when everything seems to be going wrong at once. But I'm really happy when things are happening and the air is full of good excitement."