Secretary of State Edmund S. Muskie pledged yesterday to support president Carter "all the way," but his careully worded statment did not rule out accepting a presidential draft if the Democratic Party convention spurns Carter's bid for renomination.

Muskie, who was named to his office by Carter in May, has been among those mentioned most prominently by rebelious Democrats who have mounted a drive for an "open convention" that might choose a nominee other than Carter or Sen. Edward M. Kennedy (D-Mass).

In the midst of this speculation, Muskie released a statement that said: "I accepted the appointment as secretary of state to serve the country and to serve the president. I continue to serve the president, and I will support him all the way! I have a commitment to the president. I don't make such commitments lightly, and I intend to keep it."

Although his words seemed to represent a pledge of allegiance to Carter, they were more ambiguous than Language used by Vice President Mondale who said Monday he has no intention of becoming a candidate and will do everything he can to ensure Carter's reelection.

Neither Muskie nor his aides would elaborate on the statement. However, some State Department sources and former Senate colleagues said they thought that Muskie, while believing Carter will win renomination, was exercising his veteran politician's instincts and keeping the options open.

In the meantime, the tug of war within the Democratic Party continued, with "open convention advocates -- mostly younger members of the House -- starting to form a staff and the president's cheif political operatives mounting a counteroffensive to turn back the challenge.

Carter, at a breakfast meeting yestterday with Democratic congressional leaders, said he was not concerned about the open convention movement, according to those present, and expressed confidence that he will be renominated and reelected.

Sen. Alan Cranston Reported that Carter stated emphatically that he did not expect any serious political fallout from the investigations into his brother's relationship with Libya. "I don't have anything to fear," Carter told the congressioanl leaders, "and you don't either."

At a separate meeting with a group of Democratic House members, Carter campaign director Robert Strauss passed along the same message. Those who attended the Strauss session said he strongly urged the House members to back the president, and promised that Carter would be a political asset to other Democrats this fall.

At the same time, though, the "Committee for an Open Convention," an organization formed by about three dozen House Democrats yesterday to urge convention delegates to consider presidential alternatives began to get down to business.

The committee set up an office and a telephone bank on Capitol Hill, and at least tentatively arranged to rent office space in New York across from Madison Square Garden, where the national convention will open in 12 days.

The House members spearheading the group, mainly low-seniority people who are worried about Democratic prospects in the fall if Carter heads the ticket, sent a questionnaire to every Democratic House member in an effort to line up broader support.

In the meantime, Connecticut Gov. Ella Grasso, a strong Carter supporter, nevertheless announced she had called the White House suggesting that the president release his delegates to the convention.

Grasso said she was confident Carter would win in any case, but said she felt such a gesture would head off a potentially bitter intraparty fight over rules binding delegates to a candidate.

The governor added that she had talked with Sen. Henry M. Jackson (D-Wash.), another of those mentioned as a draft alternative, but said "he didn't seem interested." Grasso backed Jackson's bid for the Democratic nomination four years ago.

The Muskie statement seemed to be exciting the most speculation because of its cryptic wording and because of the circumstances. Although White House sources had said Monday they expected Muskie to make a public declaration similar to Mondale's, sources close to the secretary had insisted Monday night that he had no intention of making any statements about his availability.

However, these sources continued, Muskie changed his mind after reporters early yesterday asked about his intentions. In these encounters, he reiterated his support for Carter, but turned aside questions about an open convention by saying that to express an opinion would involve the secretary of state in politics.

According to the sources, Muskie then decided on a written statement to avoid confusion and possible misquotations. Late in the morning, a copy of the statement was dropped unobtrusively among the press releases available in the State Department press office.

The statement prompted a barrage of questions at the daily press briefing by department spokesman John Trattner. However, Trattner said he would have no comment "under any circumstances" and added that any elaboration would have to come from Muskie.

These developments seemed to guarantee that Muskie will get an extra degree of visibility when he testifies today before the House Foreign Affairs Committee and, if the "dump Carter" movement continues, when he goes to the West Coast next week on a speaking tour.

He is scheduled to address the United Steelworkers Union convention in Los Angeles Aug. 7 and speak to an audience of prominent Californians in San Francisco the following day.

The open convention committee plans to open a "boiler room" operation today or Thursday, in which volunteers will work the telephone to reach delegates or people who know convention delegates. Three Washington Democratic activists, public relations man Hal Wolff, lawyer Fred Israel and former congressional staff aide Bob Ravilos, will direct that effort.