Leaders of the liberal political group Americans for Democratic Action (ADA) yesterday forcefully reaffirmed their support to Sen. Edward M. Kennedy's (D-Mass.) continued fight for the Democratic Presidential nomination.

But they rejected with equal force the procedural course that seems to be Kennedy's only hope for the nomination.

At a lunch just before the opening of the ADA's annual convention, to be held through this weekend at the Mayflower Hotel here, the group's president, Patsy Mink, said she was certain that the organization would repeat the Kennedy endorsement it first issued last June.

But Mink and the group's executive director, Leon Shull, both said the ADA also would be likely to oppose any effort by Kennedy to convert Democratic National Convention delegates from President Carter to the Kennedy side.Mink said the support of the "faithful delegate" concept under which delegates must vote for the candidate they have pledged to support, is a central pillar of the ADA's effort to democraticize the nominating process.

By almost every delegate count, Carter has assured himself of about 300 more convention delegates than needed to win the nomination. Thus Kennedy would have to convince some Carter-pledged delegates to switch to him in order to take the nomination.

"We are firmly committed to support Sen. Kennedy," Shull said. But we have worked hard for the rule [that delegates must honor their pledges]. You don't try to change the rule, as you would a suit of clothes, depending on the weather of the day."

Kennedy is scheduled to address the ADA convention Saturday morning, one of several speeches before friendly forums he is planning over the next few weeks as he continues his liberal challenge to Carter.

As he has done consistently since the primary season ended last week, Kennedy yesterday ignored the delegate numbers as he emphasized anew that he is "in this race right to the end."

In a series of meetings yesterday with union leaders who have supported him and with prominent Democrats on Capitol Hill he expressed his determination to fight on.

Kennedy offered his standard assessment of the Democratic race yesterday afternoon to a group of reporters who waited outside an ornate Capitol office where Kennedy met for half an hour with House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.).

"I have every intention of continuing in the race," Kennedy said. "I communicated to the speaker what I have learned on the campaign about the state of the Democratic Party around the country -- that there is a great amount of anguish and suffering among the unemployed, the elderly, young people . . . because of the misguided economic policies of this administration.

O'Neill would not repeat his half of the conversation. "Whatever I said to Ted Kennedy is private," he said.

But the second-ranking Democrat in the House, Majority Leader Jim Wright (D-Tex.), told reporters the advice he would have for Kennedy.

"I think he would serve the party well if he were to find a graceful way to get together with the president Wright said.