he Reagan administration and its deregulation chief, Christopher DeMuth, got some good marks for slowing the growth of new regulations but took it on the chin here Tuesday from officials of two former administrations for failing to make lasting legislative changes.

"You don't really change things until you change the statutes," said Simon Lazarus, associate director of the White House Domestic Policy Staff in the Carter administration.

Paul MacAvoy, a member of President Gerald Ford's Council of Economic Advisers, agreed and urged the administration to "go to work on their agenda with Congress" to assure permanent reform and elimination of some agencies. "Most of what they've done can be reversed in a year by their successors," he said.

"The problems are structural," said MacAvoy, a professor of economics at Yale University. "The agencies are doing a good job at what they have been told to do."

The criticisms and DeMuth's response were made at a panel discussion on regulatory reform held at Harvard University's Kennedy School of Government. Panel moderator Stephen Breyer, a U.S. Court of Appeals judge, noted that the panel was being held on the 95th anniversary of the founding of the Interstate Commerce Commission, the first regulatory agency. "It is the 94th anniversary of the first cry for regulatory reform," he joked.

DeMuth, executive director of President Reagan's Task Force on Regulatory Reform, said the White House was going to place "more emphasis" on statutory change the next couple of years, citing "major possibilities" in energy, communications, transportation and the financial markets.

"It's a matter of timing and strategy," he contended, "and you can't do everything at once."

DeMuth also called into question a view held by some that Republicans favor regulatory reform and Democrats don't. "I think a lot of regulatory agencies have prospered and grown under Republican administrations," he said. "Ford and Nixon gave us the Environmental Protection Agency, the Consumer Product Safety Commission, the Occupational Safety and Health Administration and affirmative action," he noted. "There are large and influential business groups . . . pressing for expansion of the regulatory state."

Lazarus, whose office in the Carter White House played a key role in legislation deregulating airlines, rails and trucking to various degrees, said the regulatory reform movement may have reached its peak, and laid some blame on the Reagan administration.