Massachusetts legislative leaders said today they would defy an order from the Democratic National Committee to postpone the state's March 4 presidential primary.

State Rep. John Murphy (D), the majority whip, said House Speaker Thomas McGee (D) has decided to let legislation delaying the election die in committee, rather than send it to expected defeat on the House floor.

The primary date has become an issue between backers of President Carter, who want it postponed until April, and Sen. Edward M. Kennedy (D-Mass.), who has personally urged the legislature to leave it unchanged.

The Democratic National Committee, citing rules requiring that primaries be held between March 11 and June 11, has threatened to refuse to seat convention delegates chosen in a March 4 primary.

But there have been indications that the White House and the national committee are seeking to avoid a showdown. A spokesman for the national committee said yesterday that no action would be taken on the Massachusetts case when the party's compliance review committee meets on Thursday in Detroit.

McGee, an announced supporter of Carter's renomination, was put in a difficult position politically when Kennedy # called him to ask that the primary date remain unchanged.

Kennedy's stated reason is that the early date will give Massachusetts voters greater influence in the selection process, but White House aides fear the senator is setting a trap for Carter, who finished fourth in the 1976 Massachusetts primary.

The effort to confine the primaries to a 13-week period faces many obstacles. The party has, in effect, conceded that it is unable to force a change in New Hampshire's leadoff primary date of Feb. 26, because Republicans control the state legislature. In Massachusetts, however, both the legislature and the governorship are in Democratic hands and the national committee has put on pressure to enforce the national party rules.

State Sen. Chester Atkins, the Massachusetts Democratic chairman, called this effort "puzzling," and said that if the postponement legislation reached the floor "it would result in a humiliating defeat for the president."