A wide-open race for the Senate's top Democratic leadership post is developing in the wake of Majority Leader Robert C. Byrd's decision to step aside after a decade as his party's chief Senate strategist.

Three senators immediately announced their intentions to campaign to succeed the West Virginia Democrat.Byrd, 70, announced on Tuesday that he will seek election to a sixth Senate term and, if he wins and his party retains Senate control, use his seniority to claim the chairmanship of the Senate Appropriations Committee.

"There is much to accomplish for my state in that capacity," Byrd said.

Many in the chamber praised the work Byrd has done as Democratic leader since 1977, noting his widely acknowledged mastery of the legislative process, but a number of Democrats also agreed it was time for a change. Byrd in recent years has been criticized by some Democrats for his leadership style and for lacking a slick television image.

With the retirement of other senior Democrats this year, Byrd will become his party's most senior member and serve as the chamber's president pro tem if Democrats retain majority control.

"I believe I have been fair, firm and honest, and I have done my best," Byrd told his fellow Democrats. "Through a decade of quiet labor I have led my party from the ambivalence of the Carter years through the extremes of the Reagan administration."

Announcing their candidacies for the leadership post, to be decided after the November elections, were Sens. George Mitchell, D-Maine; Daniel Inouye, D-Hawaii; and J. Bennett Johnston, D-La.

Several senators said there is no clear front-runner.

Inouye, who holds the Democrats' No. 3 leadership position, said his prospects are "very good" despite criticism that while serving as chairman of the Senate Iran-Contra committee last summer he permitted Lt. Col. Oliver L. North to steal the show.

Johnston, who challenged Byrd in 1986 but dropped out when it became clear he could not win, said he is "very encouraged" even though he does not yet have enough votes to win.

"No one does," Johnston said.

The majority leader of the Senate is the controlling party's chief strategist and spokesman and Johnston called the job "an opportunity without parallel."

Despite grumbling about his image, Byrd told reporters he had great confidence he could have won because "I know where the votes are."