D.C. Del. Walter E. Fauntroy said yesterday that he will become one of Sen. Edward Kennedy's national strategists to rally black voters for Kennedy in key primary states in the south.

By endorsing Kennedy and refusing to join D.C.'s pro-Carter bandwagon led by Mayor Marion Barry, Fauntroy ensured that the District's May 6 primary would not only be just a presidential contest, but also would pit his personal popularity against that of Barry.

However, as City Council member and Kennedy supporter John Ray (D-At Large) put it, the strength of such endoresements is still in doubt: "In this town, coattails are very short."

Flanked by Kennedy campaign director Stephen Smith and his deputy, Ron Brown, at a noon press conference, Fauntroy acknowleged that he has invited recriminations from his financial backers and the White House by backing Kennedy, but "I have the freedom to follow my convictions." h

Fauntroy faces no serious challenge this year in his own bid for reelection as the nonvoting D.C. delegate to the House of Representatives.

Fauntroy said he will spend most of his time in the coming months out of town, campaigning for Kennedy. Next week, he will travel to Alabama to begin organizing Kennedy supporters for forthcoming primaries there and in Georgia, Florida and South Carolina. f

Fauntroy's endoresement of Kennedy dashed the hopes of Carter strategists who had tried vigorously to build a united front of support in the city's black leadership -- even to the point of withholding White House approval of job funding and patronage appointments.

In an attempt to blunt the impact of Fauntroy's endoresement yesterday, D.C. National Committeemen John Hechinger timed hiw own Carter endorsement immediately to precede Fauntroy's press conference.

Hechinger said he had worked to change Fauntroy's mind up until Thursday night. He also said Fauntroy's choice represented a "historic rupture" between Fauntroy, himself and the rest of the Democratic hierarchy here.

Late yesterday, City Council member David A. Clarke (D-Ward 1) also endorsed Kennedy, leaving only one uncommited Democratic council member, John A. Wilson (D-Ward 2). As it stands now, six council members are backing the president, and four Kennedy.

Although he joined the Kennedy camp at a time when he said, "It looks like I'm climbing aboard a sinking ship," Fauntroy will play a high-profile role in Kennedy's southern campaign -- something that would not have been available to him had he signed on with Carter.

The delegate said he was not renouncing President Carter's record in the District. Indeed, he said both Carter and Kennedy had been friends of the district. His support for Kennedy is pegged to Kennedy's support for the poor and Carter's record on unemployment, inflation, health care and urban programs. "I think he (Kennedy) offers hope where there has been none."

Also, Fauntroy said he opposes Kennedy's Mideast policy as enunciated in his monday speech at Georgetown University. Fauntroy told Smith, Kennedy's campaign directory, that "I'm coming hard on that" in an effort to focus Kennedy's Mideast approach to a policy "of reconciliation."

Locally, Fauntroy's endorsement clearly elected Kennedy backers, who lobbied Fauntroy intensely over the past month.

A Kennedy spokesman said the senator last spoke to Fauntroy on Tuesday by telephone. By then, however, "there wasn't any doubt" that Fauntroy would come out for Kennedy, the spokesman said.

At his press conference, Fauntroy said, "I was lobbied personally by both candidates and a host of their friends."

Though any number of D.C. officials have announced presidential preferences, political observers said Barry's and Fauntroy's endoresements emerge as the most important because the two are so well known in the city.

For instance, Democratic Party chairman Robert B. Washington Jr. has endorsed Carter, but one veteran D.C. political official said, "If you ask someone in the street, 'Who's Bob Washington?' they're going to say he's the former mayor, but everybody knows Walter Fauntroy."