Sen. James O. Eastland (D-Miss.), political symbol of the segregationist South and of Dixie's former domination of the Senate, is expected to announce his retirement today after six consecutive terms.

Eastland initially denied that he would withdraw, but late yesterday his office was seeking to withdraw the denial, deferring to the announcement he is expected to make today.

State Rep. Clarence Pierce of vaiden, Miss., manager of Eastland's Jackson office, said he expected Eastland to announce today he will not seek relection. Pierce said he had not talked to Eastland personally, although Eastland had tried unsuccessfully to reach him, but had heard from Eastland's son, Woods, and Eastland's administrative assistant, Courtney pace, that Eastland would announce his retirement after 36 years in the Senate.

Pierce discounted reportes that Eastland's present health prompted the 73-year-old senator to change his mind about seeking reelection. But, he said, Eastland's health in later years may have been a consideration. "You can't escape the fact that he'll be 80 years old when (another) term would end," Pierce said.

Eastland, president pro term of the Seante and chairman of the Senate Judiciary Committee, said in October he intended to seek reelection. Since that time, three Democrats, including former governor Bill Waller, said they would challenge Eastland for the seat. Waller, in announcing his intentions Monday, said Eastland had told him in January 1976 he would not run again.

Rumors spread across Washington Jackson yesterday that Eastland would withdraw. Members of Congress and state legislation with connections to Eastland said they were convinced he would drop out of the race, but none claimed to have spoken directly with the senator.

State Rep. Jim Simpson of Long Beach, whose brother Bill is an Eastland administrative assistant in Washington, said he called his brother to find out what Eastland's plans were. "He said he wouldn't tell me what the senator has in mind, that he had committed to not saying anything." Bill Simpson reportedly wa preparing yesterday to fly to Mississippi to deliver televised tapes of Eastland's annnouncement to television stations for release today.

Eastland's retirement would make Sen. Edward M. Kennedy (Mass.) the senior Democration, and the likely new chairman of, the powerful Judiciary Comittee, a prospect that is expected to alarm many conservatives and business groups.

There could be no more dramatic symbol of the changes occuring in the Senate than the replacement of Eastland by Kennedy at Judiciary.

Eastland's retirement would leave just one old southern baron in a position of power in the Senate - Sen. John Stennis, Eastland's Mississippi colleague and the chairman of the Armed Services Committee.

Eastland's position as president protem of the Seante, largely an honorary post, would pass to Sen. Warren G. Magnuson (D-Wash.), 73, the chairmanship of Judiciary would put one of the Senate's most liberal members at the head of a committee long dominated by conservatives. Business interests are concerned about the impact of a Kennedy-run committee in antitrust legislation, which Judiciary handles.

Republican sources said Eastland appeared vulnerable in Mississippi this year even before Waller declared himself a candidate for the seat. A confidential poll done for the Republican party by Lance Tarrance of Houston, Tex., showed that a substanial number of Mississippi voters felt Eastland was too old for the job and ought to set aside for a younger person.

The poll also showed that both Democratic and Republican opponents could give Eastland a strong challenge this year.