President Carter last night laid down a strong defense of the proposed Democratic convention rule binding delegates to support the candidates to whom they are pledged, but left the door open to finessing the issue at next week's convention.

Asked about hints from his campaign chairman at the National Governors Association meeting in Denver earlier yesterday, that the Carter delegates might be released after the convention affirmed the "loyalty rule," the president replied, "I have no plans to do this."

Campaign chairman Robert S. Strauss had said in Denver: "We might do that. You never know."

Carter gave a passionate defense of the proposed rule allowing the replacement of any delegate who threatens to violate his or her candidate pledge, saying that the backers of Sen. Edward M. Kennedy (D-Mass.) and uncommitted Democrats who are challenging it are not the advocates of an "open" convention that they claim to be.

Calling that "a gross misnomer," Carter said that rejecting the rule would lead to a brokered convention in which delegates would be "induced to violate" their "signed oath or pledge" to support a certain candidate.

He said he would "put back 10 years of Democratic party progress" in shifting control from "power brokers" t the voters in primaries and caucuses.

Carter went out of his way to portray the open convention movement as an agent of the Kennedy campaign. At one point he was asked about the interest in Secretary of State EDMUND S. Muskie as an alaternative to either the president or Kennedy. "I doubt if they're interested in the promotion of Secretary Muskie,"Carter said. "I believe they're interested in the promotion of someone else."

At another point, Carter siad, "the delegates should vote the way the people back home told them to vote."

"If President Carter really believes [that] then he should let the delegates freely proclaim that support for him in August as he claims it was throughout the campaign," Kennedy spokesman Stu Shapiro said in a statement last night.

Carter's comments underlined the determination of his forces to insist on the strict loyalty rule when it comes up for a vote on Monday. But it is still not certain whether the Carter forces would then seek to heal wounds by releasing delegates, as Kennedy has already offered to do.

At a press conference in Denver last night, Gov. Bill Clinton of Arkansas, a strong Carter supporter, indicated he still thought and hoped that Carter would release his delegates as a conciliatory gesture. ,

Early yesterday the Carter backers dominated a breakfast caucus of Democratic governors and passed up an easy propaganda victory by not pressing a resolution endorsing Carter's position on the rules.

Strauss later said the president's forces "might" release the delegates once the rule is affirmed.

It was the broadest hint yet by the Carter high command that the rules controversy, which has been at the center of the frantic maneuvering by Democrats out to dump Carter, maybe mooted on the convention floor.

When reporters pressed him, the campaign chairman first backed away, saying "we have never had any discussion" about releasing delegates, as Kennedy has offered to do.

But he added : "I'm not going to do anything that indicates a lack of confidence in our delegates staying with us." And he predicted that Carter would enjoy "a net gain in strength" if all the delegates -- including Kennedy's -- were freed from the commitments they made when they were sellected.

Strauss returned to Washington late yesterday and sought to minimize his statement in Denver, asserting that he had not meant to suggest that the Carter campaign was seriously considering releasing the delegates from their pledge.

"It would break faith. It would look weak and it would be a turning back of the rules." he said.

Senate Majority Leader Robert C. Byrd of West Virginia, a group of uncommitted House Democrats and such uncommitted govenors as Hugh Carey of New York have joined Kennedy in urging Carter to relent on the rule. They claim it would reduce delegates to "robots" and cloud the legitimacy of the president's expected renomination.

Strauss claimed -- and ex-govenor Patrick J. Lucey of Wisconsin, deputy chariman of the Kennedy campaign, confirmed -- that if the Carter forces had pushed for a vote at the caucus this morning during the annual meeting of the National Govenors Association, the loyalty rule would have been endorsed by 18 of the 24 Democrats present.

Both Strauss and Gov. Bill Clinton of Arkansas, the pro-Carter causus chairman, said they did not seek a vote in the interests of post-convention party harmony.

They gave the same emplanation for the failure of the caucus to repeat the endorsement of Carter's candidacy the Democratic govenors voted a year ago. Even though 20 of the 24 Democrats present have endorsed Carter and only one -- Gov. Joseph Brednan of Maine -- is supporting Kennedy, Clinton said no vote was forced "in the interests of unity."

Aides to some pro-Cater govenors hinted they were reluctant to jump into the rules controversy, but there were indications the Carter forces had decided to pass up a short-term propaganda victory in the interests of party harmony.

"I feel very stongly we've got to look to the fall [campaign]." Strauss said. "There was no point in coming out here and flexing our muscles."

The same logic is being urged by such pro-Carter govenors as Ella Grasso of Connecticut and Jim Hunt of North Carolina in contending that Carter should release his delegates before the nomination roll call in New York, But after the loyalty rule has been affirmed.

Thus, the risk of a sudden dump-Carter rebelion would be minimized, it is argued, and the television public would be spared the spectacle of potentially "disloyal" Carter delegates being removed from the convention floor.

At this point, the option at which Strauss hinted appears to be just that -- an option. Tim Kraft, the Carter campaign manager, said in Washington that releasing the delegates after approval to the loyaly rule "has been discussed. That is all it has been -- a point of discussion. There is not a consensus. It has not been discussed with president."

Gov. Bob Graham of Florida who will nominate Carter Aug. 13, said he had heard of no such plain from "the Carter hierachy." But said Carter could release his Florida delegate without fear of losing any.

And Lucey, Kennedy's ranking representative on the scene here, in effect conceded that releasing the delegates would be a low-risk harmony gesture for Carter. He said, "of the 1,900 Carter faithful, they certainly ought to be able to hold 1,666" -- the number needed for nomination.

In his press conference, Carter referred several times to the "written pledges" of support signed by all the delegates going to the national convention. A Carter-Mondale spokesman said last night he was talking about a section of the delegate selection rules that requires prospective delegates or alternates to submit "a signed pledge of support for the presidential candidate the person favors" at the time the person filed his candidacy.

Meanwhile, party officials in a sampling of 14 key states reported fewer than 20 Carter delegates leaning toward a vote for an open convention, and even those are likely to vote for Carter for renomination.

The "slippage" amounts to an estimated seven to 10 delegates out of 70 pledged to Carter in Michigan, perhaps one or two of 74 in Florida and a maximum of six of 19 in Colorado.

The officials described the apparently tenacious Carter strength with varying degrees of enthusiasm, and some added. "Of course, anything can happen in politics."

Many echoed the sentiments of Barton J. Gordon, executive director of the Tennessee state party. "This delegation is very solid for Carter . . . Regardless of whether they're [personally] strong for him or not, they feel a strong commitment to the people of Tennessee and the [primary] mandate."

Olivia Maynard, cochairman of the Michigan state party said, when the open convention furor hit about a week ago. "There were some Carter delegates who were thinking seriously about voting against the rule. But I have not heard of others since then." She said seven to 10 delegates, of 70 pledged to Carter, were wavering.

But she added, "My sense it that even those who are against the rule, will still vote for Carter on the first ballot."

Carolyn Schisler of Illinois, a state central committeewoman, dismissed "these silly efforts to change the rules midway through the ball game . . . We're fed up with the select few who want to change the rules to suit them."

One argument against the rule has been that conditions have changed since the primaries. But even in that long-ago first primary state of New Hampshire, the point doesn't seem to be selling. Ricia McMahon, executive director of the state party, reported that some of the Carter delegates may vote against the president on some platform issues, but not on the open convention issue.

"They'll stick with the president," she said. "Even if it were open. I don't think our delegation's vote would change."

A number of party regulars have argued that Carter could strengthen his candidacy since he seems assured of the nomination, by agreeing to the open convention strategy and unifying the party.

Wisconsin state party chairman Joseph Checota plans to hop around the state Tuesday in a small plane and lobby the 48 Carter delegates to support an open convention. He opposes Carter because of the adverse effect his plummeting fortunes are likely to have on the reelection races of the state's incumbents, such as Sen. Gaylord Nelson, and on control of the state legislature, he said.

But he added, if Carter is nominated, "he will be a stronger candidate" if the convention is open. At this time however, he could point to no softening among any Carter delegates.

In lieu of a resolution on the rules controversy or a reendorsement of Carter, the Democratic governors contented themselves with a unanimous statement condemning the Republican platform. The statement offered by Gov. Brendan Byrne of New Jersey said the GOP manifesto "seeks the withdrawal of our national government from the most basic areas of national concern" and promises "a panacea for all problems [in] . . . ill-considered tax reductions . . ."

By way of response, the Republican governors unanimously approved a statement condemning "the erosion of presidential leadership under Mr. Carter" and blaming him for weakening national defense, crippling the economy, allowing the growth of government and continuing dependence on foreign oil.

The notable difference between the statements was the frequent Republican pledges of support for Ronald Reagan and the absence of Carter's name from the lengthy Democratic resolution.