The Environmental Protection Agency has failed to evaluate properly the environmental and health impact of numerous federal projects, from nuclear power plants to offshore oil drilling, the agency's inspector general said yesterday.

More than half the EPA's required reports were issued either late or not at all, the inspector general said.

Acting Inspector General Charles L. Dempsey also charged in a report yesterday that the EPA's Office of Federal Activities lied to senior agency officials by reporting that 90 percent of certain environmental reviews were completed on time, although the actual figure was 25 percent.

Dempsey said the office "failed to fulfill its obligations," largely because "established procedures were ignored" and the office suffered from "a lack of direction and management."

The Office of Federal Activities is responsible for monitoring the impact of federal government projects and registering objections with the appropriate agencies. Dempsey's audit followed earlier allegations that reports by staff scientists often were rewritten, delayed or canceled, particularly if they raised environmental objections to Reagan administration programs.

The audit report said that only 35 of the EPA's 74 reviews of major federal actions, or 47 percent, were completed on time. The remaining 39 reviews were sent out late or not at all, with 22 still overdue as of February and seven of them more than a year past due. Dempsey's report said the responsibility rested on the former office director, Paul Cahill, a political appointee from California who resigned last month after the audit began. Cahill's deputy, Louis J. Cordia, also resigned last month after it was confirmed that he had compiled "hit lists" of EPA employes to be hired, fired or transferred according to their political leanings.

Rep. Mike Synar (D-Okla.), whose House Government Operations subcommittee is investigating the office, said that while "some managers were compiling political hit lists, they were abdicating their responsibility to protect public health and the environment." He charged that several reports were "halted" because "such comments could have been embarrassing to the administration."

In one case last April, the office failed to submit comments on a draft environmental impact statement for proposed oil and gas drilling off the coast of Massachusetts, the report said. Several environmental groups sued the EPA for failing to provide the comments to the Interior Department.

The lawsuit disclosed that EPA regional officials had given Cahill critical comments on the proposed drilling five months earlier, calling the environmental impact statement misleading and incomplete. But although Cahill was briefed on the issue, the report said, he did not forward the comments to Interior by the April deadline.

In another incident, an EPA staff member prepared comments on proposed drilling in the Gulf of Mexico before the deadline last November, but Cahill's office never sent the comments to Interior. All told, the audit found, staff comments had been prepared in 10 of the 22 cases where Cahill failed to release a report.

The audit also found that many of the files in Cahill's office were incomplete, and that in 66 cases they did not contain all the comments made by agency scientists. Staff members told the auditors that "documents would go into Cahill's office and not be seen again." They also said the proposed comments "were either delayed, changed or not sent out by Cahill's office."

Acting EPA Administrator Lee L. Verstandig said he welcomed the report and was moving to adopt Dempsey's recommendations on correcting the problems.