The independent counsel investigating former housing secretary Samuel R. Pierce Jr.'s. operation of government grant and subsidy programs was given additional authority yesterday to investigate whether Pierce lied to Congress and violated the law in dealings with his former law firm and former executive assistant.

In an order to independent counsel Arlin M. Adams, the federal appeals court here also authorized Adams to scrutinize the Department of Housing and Urban Development's multifamily housing coinsurance program, under which HUD guarantees mortgages for apartment projects.

Adams was appointed in March to investigate allegations that Pierce and other HUD officials showed favoritism in awarding lucrative rent subsidies under the Moderate Rehabilitation program. In July, the court gave Adams jurisdiction to investigate two other programs, the Urban Development Action Grant program and Pierce's discretionary fund for technical assistance and special projects.

Yesterday's ruling follows a House subcommittee request, also made in July, for Adams to expand his inquiry into the additional three areas. In August, Adams asked Attorney General Dick Thornburgh to seek a court order that would allow him to widen the probe. By law, any request for expansion of the independent counsel's inquiry must be made through Thornburgh to the special three-judge panel that appointed Adams.

Since August, a Justice Department official said, the department has been struggling with legal questions about the independent counsel's jurisdiction.

Pierce's attorney, Paul L. Perito, issued a statement saying: "The order expanding jurisdiction breaks no new ground. . . . The independent counsel already had jurisdiction over most of the matters that were included. We view the court's approval as a technical mechanism for protecting the jurisdictional mandate of the independent counsel.

"We are fully confident that, at the conclusion, the independent counsel will find Secretary Pierce did not violate any federal laws or regulations."

The court's order yesterday authorizes Adams to look into any dealings between Pierce, his former law firm Battle, Fowler, Jaffin & Kheel, and his former executive assistant at HUD, Lance Wilson. Adams will also attempt to determine whether Pierce committed perjury in his testimony before a House Government Operations subcommittee.

The full Government Operations Committee issued a report in November finding that "at best, Secretary Pierce was less than honest and misled the subcommittee about his involvement in abuses and favoritism in HUD funding decisions. At worst, Secretary Pierce knowingly lied. . . . "

Among other HUD grants, the report raised questions about the awarding of a Florida housing project to a client of Pierce's former law firm after the law firm contacted Wilson for help.

The managing partner of Battle, Fowler has previously said that his firm engaged in nothing improper. Wilson could not be reached yesterday for comment on Adams's probe.