A Democratic National Committee panel yesterday firmly rejected efforts by Iowa and Maine to hold their presidential delegate selection caucuses earlier than the newly tightened party rules allow.

The rejections may be the first round of a fight that could wind up in a credentials battle at the party's 1984 national convention.

Today, the Compliance Review Commission is expected to take the same unyielding position toward New Hampshire, which has changed the date of its first-in-the-nation primary to ensure that it takes place a week before a non-binding "beauty contest" presidential preference vote in Vermont scheduled for next March 6, the original date of the New Hampshire primary. Vermont wants its contest the same day as its annual town meetings.

The problem is that the election laws in these states now conflict with national Democratic Party rules. Maine, Iowa and New Hampshire are vowing to proceed with their early delegate selection efforts in the face of the national party's threats to refuse to seat their delegates at the convention in San Franciso.

Maine Gov. Joseph E. Brennan, who argued before the commission yesterday that his state's case is "stronger than Iowa's and New Hampshire's," said he was willing to enforce his state's law and and carry the fight for delegate credentials to the Democratic National Convention floor in 1984, if necessary.

In an effort to compress the presidential nominating period, the Democratic Party established a March 13 to June 12 "window" during which all primaries and caucuses are to be held in 1984. However, it granted waivers allowing New Hampshire to have its primary on March 6 and Iowa to have its caucuses on Feb. 27 so they could remain first.

But then Vermont moved to have a non-binding presidential preference vote March 6, the same original day as the New Hampshire primary.

New Hampshireites, jealous of being first, moved their primary back a week in violation of the rules. The state legislature passed a law requiring that theirs must be the first presidential vote in the nation and interpreted it to include beauty contests as well as delegate-selection votes.

Iowa does not care about Vermont's decision but it does care about New Hampshire's. The Iowa law requires that the state hold its presidential delegate selection caucuses no fewer than eight days before any presidential event anywhere. So if New Hampshire moves, so must Iowa.

Maine party officials argued that they have a 250-year tradition of holding town meetings in mid-March and that party presidential caucuses must be held before them. So Maine has just passed a state law decreeing that the initial presidential delegate-selection caucuses will be held March 4, nine days before the party's "window" opens.