Consumer advocates charged Saturday the Federal Trade Commission has failed to enforce antitrust laws under President Reagan, giving business too much of a free hand in mergers that are unhealthy for consumers and the economy.

Public Citizen, a consumer and environmental interest group founded by Ralph Nader, noted in a new study that the United States is going through an unprecedented wave of corporate mergers and acquisitions."The economy is being swept by merger-mania, yet the Reagan FTC refuses to enforce the law," said Joan Claybrook, president of Public Citizen.

"The takeover of Kraft by Phillip Morris is just the most recent example when the FTC stood by and did nothing to the detriment of consumers," she said. "In their flagrant refusal to enforce the law, FTC Chairman James Miller and Daniel Oliver are the James Watt and Anne Burford of anti-trust."

In the early years of the Reagan administration, environmental activists scorned Watt, the former interior secretary, and Burford, the former head of the Environmental Protection Agency, for actions they felt were harmed more than helped the environment.

The study concluded the 10 largest mergers in American history took place during the Reagan administration and none were challenged by the FTC.

"We are living through the biggest merger boom in history, yet the antitrust cop has been pulled off the beat," said Michael Waldman, co-author of "The Absent FTC: Non-Enforcement of Antitrust Law in the Age of Merger-Mania." Waldman is legislative director of Public Citizen's Congress Watch. Co-author Daniel Atkins is a research associate at the organization.

The report also said the FTC has brought only 13 cases against mergers during seven years of the Reagan administration compared with 22 cases in the four years of the Carter administration.

Further, the FTC failed to bring even one case against companies suspected of a wide variety of anti-competitive behavior, such as price fixing between manufacturers and retailers, price discrimination or interlocking boards of directors, the study said.

And whereas the Carter administration filed complaints against such corporate giants as Ford Motor Co., DuPont and General Motors, the FTC under Reagan has focused only on obscure, smaller businesses, according to the report. Those firms include Smitty's Supermarkets and the Oklahoma Optometric Association.

"Congress and the next president should revitalize the agency and ensure that consumers are protected through full enforcment of the law," Atkins said.