The D.C. Carter-Mondale campaign headquarters opened yesterday in the same downtown location that housed the local primary headquarters for Sen. Edward M. Kennedy this spring, but the split between the two camps still divides the District's Democratic Party.

While Mayor Marion Barry and other Carter supporters spoke of unity between the Carter and Kennedy forces, City Council member John Ray, who arrived late, was the only well-known former Kennedy supporter to attend the noontime opening that attracted a crowd of about 100 to the headquarters at 425 13th St. NW.

D.C. Del. Walter E. Fauntroy, an early Kennedy supporter, was absent and attending instead a House-Senate conference committee. Anita Bonds, one of the best nuts and bolts political operatives in the city, coordinator of Kennedy's successful primary campaign and Barry's own deputy campaign manager in 1978, said she was not invited to the office opening.

Kennedy handily won the city's May 6 Democratic primary, and 12 of Washington's 19 delegates to the Democratic National Convention were Kennedy supporters.

But Barry and school board member Barbara Lett Simmons, who is the local Carter-Mondale campaign manager, said they were unaware of any lingering hard feelings.

"We expect to have the Kennedy people with us," said Mikel Miller Carter's deputy campaign manager for the East Coast, the highest-ranking campaign aide to attend the opening. "You can't expect everybody to be here on the first day." Health and Human Services Secretary Patricia Harris also attended.

Although the District has only three electoral votes, many local and national political observers view the District as a bellwether for measuring black sentiment and blacks have been one of the principal constituencies in Carter's political base. Carter's chances of defeating Ronald Reagan are considered slim if he does not have strong black support.

Barry told the crowd that a new Carter headquarters at an old Kennedy one symbolized a united party. "We're now all coming together to elect a great Democratic president and a great Democratic vice president," the mayor said to loud applause and cheers.

But Ray told a reporter afterwards that there will be little or no unified fund-raising or campaigning between the local and national Democratic tickets that characterized the election four years ago because of a lack of support for Carter among some local campaign workers.

"We still have some disenchanted Kennedy supporters who are not willing to participate in a unified effort," he said. Ray, who is running to retain his at-large City Council seat, said some of his workers who supported Kennedy have refused to distribute campaign literature for the President or to make financial contributions to the presidential campaign.

A source close to City Council member John A. Wilson (D-Ward 2), who is also running for reelection from Ward 2, the area surrounding downtown, said that campaign would print sample ballots showing only Wilson's name because of the lack of unity in the party. Four years ago sample ballots contained the entire Democratic tickets, both national and local.

"People are not gung-ho for the Democratic Party top to bottom," said the source, "So all the campaign stuff will be John Wilson only."

Fauntroy's reelection campaign has not encountered any lack of support for Carter, said a spokesman for the delegate.

Bonds, who is now running Ray's campaign, said all her energies would go into reelecting the council member.