Sen. Howell Heflin (D-Ala.), who cast the decisive vote against judicial nominee Jefferson Beauregard Sessions III in the Senate Judiciary Committee, was labeled a "traitor" yesterday by the daily newspaper in Sessions' hometown of Mobile, Ala.

"U.S. Sen. Howell T. Heflin became the Benedict Arnold of Alabama Thursday when he put party before principle and cast the key vote to reject the federal judicial nomination of U.S. Attorney Jefferson B. Sessions III of Mobile," an editorial in the Mobile Register said.

Heflin "committed the ultimate act of treason" when he "toed the party line and established himself as simply another political hack who can be swayed by the liberal Eastern Establishment," the editorial said.

The newspaper company caused a stir in March when Eddie Menton, city editor of its afternoon Mobile Press, testified on Sessions' behalf before the Judiciary Committee. Menton has said people in Mobile were "incensed" about criticism of Sessions and that he testified about the prosecutor's "good reputation."

Sessions, accused of making racially insensitive remarks, is the first of President Reagan's judicial nominees to be rejected by the committee. Heflin joined the panel's other seven Democrats and two moderate Republicans in the 10-to-8 vote.

Heflin, a soft-spoken conservative and former chief justice of the Alabama Supreme Court, frequently supports Reagan nominees and received hundreds of letters and calls from Alabamians supporting Sessions. He told the panel that he had agonized over the vote but was troubled by inconsistencies in Sessions' testimony.

"This is not an easy vote for me, and it will be one that many will disagree with, particularly in my home state," Heflin said. "But as long as I have reasonable doubts, my conscience is not clear and I must vote no."

Mobile is the home base of Sen. Jeremiah Denton (R-Ala.), who recommended Sessions for U.S. attorney and the federal judgeship. Denton, who is running for reelection, said Thursday that there was "a political conspiracy" in Alabama to discredit Sessions.

The Register editorial said Heflin "might very well become the darling of the Washington Establishment . . . . But for Heflin to toe the line with the Kennedy faction in the Senate is disgraceful -- and his action undoubtedly cost him many friends and supporters in southwest Alabama."