Mayor Marion Barry will not be at the head of the D.C. delegation to the Democratic National Convention when is assembles on the floor at Madison Square Garden in New York next month.

Neither will Del. Walter E. Fauntroy, City Council Chairman Arrington Dixon nor local Democratic Party leader Robert B. Washington Jr.

Leading the delegation instead will be City Council member John L. Ray (At Large), a man who was virtually unknown to District voters three years ago.

It is unusual though not unprecedented, for a convention delegation not to be headed by high-ranking local officials or party leaders.

The Maryland delegation to this year's convention is being headed, for example, by Gov. Harry Hughes. The Virginia contingent is being led by Richard Davis, the mayor of Portsmouth and chairman of the state's Democratic Party. Fauntroy led D.C. delegates at both the 1972 and 1976 conventions.

To some extent, the choice of a reltively minor official to lead the D.C. group reveals the Carter vs. Kennedy split in the local party. Barry, Dixon and Washington are all supporters of President Carter, while 12 of the 19 members of the delegation are pledged to Sen. Edward M. Kennedy.

That left the Kennedy majority -- which decided to vote as a bloc against the Carter delegate forces to elect a pro-Kennedy chairman -- a choice between Ray and Fauntroy, both of whom reportedly actively sought the post.

The decision to elect Ray kindled bad feelings between the two men, party sources say, and perhaps signaled a larger role in the city's political life for Ray, who three years ago could have been called "John who?"

The Kennedy faction chose Ray at a lengthy District Building meeting three weeks ago. According to sources, Fauntroy's bid was rejectd in part because some delegation members held long-standing grudges against him, and also because others felt Ray had worked harder than Fountroy for the local Kennedy effort leading to the May 6 D.C. primary.

"The feeling was that John was always around while Walter sometimes wasn't," said one member of the delegation, who nevertheless supported Fauntroy for the post because of his office and his role in Kennedy's national campaign.

Along with City Council member Betty Ann Kane and former Barry aide Anita Bonds, Ray ran the Kennedy effort in the District Fauntroy, on the other hand, spent a considerable amount of time campaigning for Kennedy in other cities, including Milwaukee, where he brought down a packed house with a stirring rendition of "The Impossible Dream."

Sources said Fauntroy called Barry, a member of the Carter camp, for advice when it became clear he would lose the fight for the chairman's post. Barry reportedly suggested that he and Fauntroy be cochairman of the delegation, but Fauntroy rejected the idea. Sources said Fauntroy also rejected the notion of being a cochairman with Ray.

In a telephone interview yesterday, Fountry took credit for leading the Kennedy forces to victory in the May 6 primary, and acknowledged that he had sought to be named chairman of the delegation.

Other sources said, however, that a factor in the choice of Ray over Fauntroy was Fauntroy's behavior at the last two national conventions. They accused Fauntroy of having worked out deals on behalf of the earlier delegations without consulting their members.

Ray's selection is further indication that the council member, long viewed by fellow council members and other observers as a virtual stand-in for Barry, is attempting to strike out on his own.

Ray has been associated with Barry since 1978, when he threw his support in the mayor's race to Barry, and Barry in turn lobbied to have him named to the City Council. But recently, Ray, by his own admission, has "shifted into second gear."

"I had to let people know I'm my own man," he said in an interview yesterday.

Ray faces opposition from only one little known candidate, Raymond Powell, in his bid this fall to retain his council seat. Last week, he collected 12,000 at a glittering fund raising event at the Fairfax Hotel, which featured claims on the half shell and an open bar.

"I didn't kick Walter out," he said of the dispute with Fauntroy. "The delegates voted for me."