Members of the Democratic National Committee, gathering for the first time since the stormy winter session that elected Paul G. Kirk Jr. as chairman, breezed through a series of preliminary votes here yesterday with many onetime dissidents expressing a new willingness to follow Kirk's leadership.

In contrast to the gloomy mood that prevailed last winter, Democrats yesterday sounded an upbeat note on the opening day of three days of meetings.

The DNC executive committee endorsed Kirk's proposal to eliminate the 1986 midterm convention and supported his $23.1 million budget to carry the party through the 1986 midterm elections.

The only sour note yesterday came when it was announced that Louisiana state Rep. John W. (Jock) Scott, a DNC member, was switching to the Republican Party, but Democratic leaders quickly dismissed Scott as an "opportunist."

Most of the votes taken yesterday must be ratified later this week by the full DNC. But the opening day set the tone for a harmonious session that would allow the party to present just the image that Kirk wants -- one of an organization concerned less with internal divisions and more with winning elections.

"The differences that existed are now being seen as what they are -- minor differences" when compared with those between Democrats and Republicans, said New York State Democratic Chairman Laurence J. Kirwan. "We're not going to mine our own harbors."

The DNC black caucus, embittered in February by Kirk's refusal to back their choice for party vice chairman, yesterday overwhelmingly endorsed the chairman's nominees for the Fairness Commission, even though Kirk rejected the Rev. Jesse L. Jackson's choice.

Jackson, whose complaints about the presidential nominating rules last year helped create the commission, wanted former Atlanta mayor Maynard Jackson to head the group, but Kirk chose former South Carolina Democratic chairman Don Fowler.

"The past is the past and the future is what we are going to do as leaders in suggesting the tone and the course" the party will take, said Caucus Chairman C. Delores Tucker of Pennsylvania. The announcement of the defection by Louisianan Scott came from the Republican National Committee. "Rep. Scott represents millions of Democrats throughout the country who have felt abandoned by their own party and are turning to the Republican Party for leadership and direction," Republican National Committee Chairman Frank J. Fahrenkopf Jr. said.

DNC spokesman Terry Michael said, however, that "Jock Scott's timing couldn't be worse. There is a broad consensus in our party to affirm our commitment to the mainstream concerns of the American people, while the Republican Party continues to drift to the right-wing fringe."

In two other votes, the executive committee urged Congress to extend general revenue sharing beyond the 1986 fiscal year and opposed President Reagan's repeal of the federal deduction for state and local taxes.