The cavernous International Ballroom at the Washington Hilton Hotel was only about two-thirds full last Friday night. Despite the presence of three of the bluest blue-chip speakers the Democratic Party can muster these days, the D.C. Democrats' biennial Kennedys-King Day dinner fell short of being electrifying.

The most ringing exhortation, in fact, came not from the national talent but from Mayor Marion Barry, who delivered his message like a country preacher.

"Last November, the Democrats had some hard times nationally," Barry shouted. "But Washington, D.C., was one of the five states that stood up strong for our nominess, President Carter. So let's hang in, keep going and keep on keeping on."

Barry's call to perseverance was met with only a weak ovation. At one point he had accused the crowd of being so quiet that they were "sounding like Republicans." Indeed, they did sound like Republicans.

The dinner and related activities, including workshops on practical politics for aspiring local candidates, commemorated three liberal martyrs of the 1960s -- John F. Kennedy, Robert Kennedy and the Rev. Martin Luther King Jr. As usual, the event attracted national political figures: Sen. Edward M. Kennedy (D-Mass.), Democratic National Committee Chairman Charles T. Manatt and the Rev. Martin Luther King Sr.

But this time around, the atmosphere was different. Nationally, the Democratic Party generally is acknowledged to be in a shambles, having been routed in last November's elections.

But this time around, the atmosphere was different. Nationally, the Democratic Party generally is acknowledged to be in a shambles, having been routed in last November's elections.

"It makes a difference," said Robert B. Washington Jr., who headed the local party for five years until earlier this month. With Ronald Reagan in the White House and the Republicans in control of the Senate, there is less access and influence for local Democrats.

Paradoxically, the D.C. Democratic Party is as strong as every, enjoying nearly a 9-1 edge in registration over Republicans. While more than 2,000 D.C. Democrats jumped ship to vote for John B. Anderson in last year's GOP presidential primary, Democratic leaders say they are confident that they will lure those voters back.

So there is little need here for the fervor of rebuilding that Democrats elsewhere feel. At the dinner, however, there was a king of sad-eyed nonchalance among the Democrats, which showed in response to the jokes Kennedy used to begin his remarks:

"It's good to get away from Capitol Hill . . . if only for a while. Jesse Helms has been throwing his weight around a lot lately.

"Alexander Haig is drawing up a new order of succession to the presidency -- and I'm trying to get my name on it."

Kennedy, perhaps the ultimate keeper of the Democratic flame (especially since Carter's departure from the political scene), acknowledged that his win in last May's D.C. Democratic Primary was his "greatest victory." Of all the primary states, the little District of Columbia, with its 12 convention delegates, was where Kennedy did best.

Kennedy plowed on with the litany of issues on which he urged Democrats to resist the Reagan agenda -- civil rights, defense spending, "foolish and insensitive" budget cuts -- and ended by quoting from his own "keep the faith" speech at last summer's Democratic convention, when he electrified the party by vowing that "the dream shall never die."

Kennedy was scheduled to be the after-dinner speaker, but he asked to rearrange the program so that he could catch an early plane for Massachusetts. rThus, he delivered his speech before dinner. By the time some tardy Democrats arrived, Kennedy already had spoken. Barry arrived just in time, having been summoned repeatedly by a worried political aide.

Manatt, in his talk, upped the verbal ante, calling Reagan and his team "the most highly ideological, right-wing administration that this country has faced in years and years and years," and calling the president's fiscal cuts "the most political, most racist budget ever presented to this country by any administration."

One of the reasons for the small turnout, it seems, was that Kennedy, Manatt and King were competing with a farewell dinner across town for former school superintendent Vincent E. Reed. That kind of event might not always have been real competition for Kennedys-King Day, but this year it was.