The Reagan administration is preparing to salt the board of the controversial Legal Services Corp. with conservatives, including three from the Pacific Legal Foundation, a group that has often been in combat with legal services units in the past.

Pacific Legal Foundation, which until recently included presidential counselor Edwin Meese III on one of its advisory boards, is a non-profit law firm that describes itself as dedicated to free enterprise, economic growth and limiting the role of government. It is a first cousin to the conservative Mountain States Legal Foundation, which Interior Secretary James G. Watt headed before he joined the administration.

Sources in the legal services community say that President Reagan plans to nominate persons connected with the Pacific Legal Foundation to fill three positions on the board. By law, two positions must go to poor people. All 11 positions are up for Reagan to fill because the terms of President Carter's appointees have expired.

Ronald A. Zumbrun, president of the foundation, is expected to become chairman of Legal Services. Marc Sandstrom, a banking lawyer who is foundation vice chairman, and William F. Harvey, an Indiana University Law School professor who serves on one of the foundation's advisory boards, are expected to become Legal Services board members.

Reagan had urged Congress earlier this year to abolish the Legal Services Corp., which distributes federal funds to individual programs around the country to provide legal assistance to the poor. Reagan has long opposed Legal Services; as governor of California, he fought with some of its units.

Congress so far has refused to eliminate Legal Services although its budget has been cut by about 25 percent from $321 million in the 1981 fiscal year to $241 million this year.

The nominations are subject to Senate confirmation.

Members of the legal services community have already expressed concern about the rumored appointments.

Dan Bradley, the current president of Legal Services, has fought the plan to abolish the agency and has said he is disappointed with the rumored choice of Zumbrun.

Zumbrun, who was not available for comment, was deputy director of legal affairs for the California Department of Social Welfare while Reagan was governor before he joined the Pacific Legal Foundation in 1973. The foundation has largely been involved in lawsuits protesting government regulations, both federal and state.

Al Meyerhoff, regional counsel of California Rural Legal Assistance, says that his organization was regularly involved in litigation with Zumbrun while he worked for the welfare department.

Robert Gnaizda, a partner in Public Advocates, a San Francisco-based public interest law firm, called Zumbrun "one of the chief legal architects of Reagan's anti-poor actions, particularly in denying health and welfare benefits to the poor. If Zumbrun carries out the philosophy that was in evidence then and is in evidence now, he will quickly dismantle Legal Services either directly or through setting up barricades to services."

Katharine Krause, executive director of the Legal Aid Foundation of Los Angeles, said, "It's a tragedy for the Legal Services Corp. and a tragedy for poor people. Not a day goes by that we don't discuss him, and there is a tremendous fear about the effect he and a conservative board will have."

Harvey confirmed that he has been notified by the White House that he will be nominated. He describes himself as a strong Reagan supporter--"vigorously so...I come from the Reagan side of the Republican Party."

Harvey has argued in opposition to court-ordered busing as a means of school desegregation. On behalf of the Pacific Legal Foundation, Harvey also wrote one of the briefs for the Supreme Court in the controversial reverse-discrimination suit brought by Allan Bakke against the University of California Medical School at Davis.

Sandstrom, who is executive vice president and general counsel of San Diego Federal Savings and Loan, was not available for comment.

The board positions are part-time and pay no salary.