Sharon Pratt Dixon, a longtime D.C. Democratic activist and a vice president of the Potomac Electric Power Company (Pepco), plans to step up her long-shot bid for the chairmanship of the Democratic National Committee today at a winter meeting of state party chairmen in the Virgin Islands.

Dixon, 40, the D.C. Democratic national committeewoman, contends that a black woman with business experience would best be able to pull together the shell-shocked Democratic Party, in the wake of President Reagan's 49-state reelection victory over Democrat Walter F. Mondale.

"You need someone who is a Yuppie, a free-enterprise type, but who is also a beneficiary of the New Deal coalition," Dixon said.

Several prominent black mayors, including Coleman Young of Detroit, Ernest N. Dutch Morial of New Orleans, Harold Washington of Chicago and Richard Arrington of Birmingham, have agreed to support her, according to Dixon.

However, Jesse L. Jackson, who endorsed Dixon for party chairman last July when it briefly appeared that Chairman Charles T. Manatt would be ousted, hasn't said whether he will continue to support Dixon.

"A lot of people are playing it loose," said Dixon, who will be the guest of honor at a reception this afternoon on St. Thomas, at the start of a weekend meeting of the Association of State Democratic Chairs.

Ivanhoe Donaldson, chairman of the D.C. Democratic State Committee, and Daria Portray Winter, the committee vice chairwoman, will be hosts at the reception, which will be paid for either with private contributions or D.C. state committee funds.

Donaldson, a top political adviser to Mayor Marion Barry, said through an aide yesterday that he supports Dixon because it is important to choose a party chairman who "pays the mortgage from a regular paycheck" and who can appeal to a broad range of factions within the party, including businessmen, women and minorities.

Donaldson recently incorporated a Dixon for Chairman committee in the District with the help of attorney Peter F. O'Malley, a member of the Pepco board of directors, and Rachelle Horowitz, director of the American Federation of Teachers' Political Action Committee. Dixon hopes to raise about $40,000 for her campaign for chairman.

Manatt said he took the job as chairman four years ago with the presumption that he would serve one term. But he said recently he would make a final decision by the end of this month, after conferring with the state chairmen and congressional leaders. A number of possible candidates for the job have emerged, including outgoing Gov. Scott Matheson of Utah, former congressmen Bob Kreuger of Texas and John Cavanaugh of Nebraska, and retiring Sen. Paul E. Tsongas of Massachusetts.

Rep. Michael D. Barnes of Montgomery County is being pushed for the post by a number of prominent Maryland Democrats, including Sen. Paul S. Sarbanes, Gov. Harry R. Hughes, state party Chairman Howard Thomas and committeeman Lanny Davis.

A spokesman for Barnes said that if asked to assume the post, Barnes "would seriously consider it," but that he is not actively seeking it. Barnes does not plan to go to St. Thomas.