Mayor Marion Barry yesterday replaced Bernice Just as chair of the D.C. Parole Board, appointing D.C. Department of Corrections official Walter B. Ridley to the chairmanship and a six-year term on the board.

Just, who could not be reached for comment, is to remain on the three-member board. Ridley was appointed to take the seat of the Rev. H. Albion Ferrell, who has been on the board since 1962.

The announcement of the appointment, effective June 17, did not give a reason for the mayor's decision to replace Just as chair, but sources pointed to criticism of the board on Capitol Hill and by the U.S. attorney's office as factors in the change.

Annette Samuels, Barry's press secretary, said she did not know why Just was replaced as chair but that she "has been there for quite some time."

Ridley, administrator of youth facilities in the corrections department since 1980, also has served in other administrative jobs at Lorton and in drug rehabilitation programs for offenders since 1972.

The parole board has come under attack in the last two years by Sen. Arlen Specter (R-Pa.), chairman of the Senate Appropriations subcommittee on the District, and from U.S. Attorney Joseph E. diGenova, who both charged that the board has been lenient in releasing prisoners from the District's Lorton Reformatory.

Specter pushed successfully for major changes in parole board guidelines on release and revocation of parole, establishing stricter criteria for parole and requiring revocation in some cases such as when the board has evidence of drug use by a parolee.

"Criticism from Specter and from the U.S. attorney clearly led to the decision to have a new chairman," according to one source. "The mayor had been under considerable pressure" to appoint someone who would take a harder line on parole, that source said.

Ferrell made some controversial statements on the parole board at hearings held last year, including the comment that the board "has no right" to continue incarceration of certain persons after they had fulfilled objectives set forth for them. Specter objected to the idea that convicted prisoners have a "right" to be released on parole before their full sentence is completed.

Specter said last December that he expected changes in the membership of the board. Asked about the comment at the time, Just said it was "the mayor's decision" to make, and she declined to say whether she wanted to stay as chair.

Yesterday's announcement, released late in the day, stated that Just "expressed her delight" at Ridley's appointment. Attempts to reach her at her office and home were unsuccessful.

Barry commended Just for "excellent service."

Ridley also could not be reached for comment.