Ronald L. Plesser, 59, a leading authority on federal privacy law and information policy for the past three decades and a partner in the Washington office of the Piper Rudnick law firm, died of a heart attack Nov. 18 at Dulles International Airport.

Mr. Plesser's work on information policy helped set the evolving standards for privacy in an era of computer databases, new communication technologies and the Internet.

He worked first with Ralph Nader's Center for the Study of Responsive Law in the early 1970s, where he compiled a comprehensive catalogue of the shortcomings of the 1966 Freedom of Information Act. His work formed the basis for Congress's 1974 overhaul of the statute, which made it easier for the public to gain access to government records.

"He was without question one of the real pioneers in the privacy field," said Marc Rotenberg of the Electronic Privacy Information Center, a public interest research center in Washington.

Mr. Plesser also litigated numerous cases under the Freedom of Information Act. He represented NBC reporter Carl Stern in a suit that uncovered the first evidence of COINTELPRO, the FBI's program to disrupt the civil rights and antiwar movements.

He also won a landmark appellate decision in Vaughn v. Rosen that established procedures for lower courts to follow in Freedom of Information Act cases.

In 1975, Mr. Plesser became general counsel of the Privacy Protection and Study Commission, where he oversaw government-wide compliance with federal privacy law.

Jerry Berman, president of the Center for Democracy and Technology, called Mr. Plesser "the expert at the table" who knew the law, the technology, the players and how to build consensus on privacy policies for cable subscribers, cell phone users and video renters.

"Ron Plesser not only educated all of us about threats to privacy in the computer age, but also of the social value of new technologies in our lives. He thus saw the need to find policy solutions that both recognized the value of computer technology in government and commerce and established privacy and civil liberties protections for citizens and consumers," Berman said.

Often quoted in the national and trade press, Mr. Plesser warned of the dangers of combining government and commercial databases. In 1983, he told Computerworld magazine, "I don't oppose computer matching totally, but I am troubled that there is no institutional control within the government on this issue.

"If someone in the government came up to you on the street and demanded to see your bank account, that would obviously be an illegal search and seizure. But if the government can get that information from a computer, somehow that seems to sanitize it, to legitimize it."

Mr. Plesser was born in Queens, N.Y., and graduated from George Washington University. He received a law degree from the National Law Center at GWU in 1970.

In 1988, after working for the Nader organization, he joined the Washington office of the firm now known as Piper Rudnick, where he represented trade associations and database publishing companies and testified numerous times before Congress and world regulatory organizations.

Mr. Plesser was past chairman of the Individual Rights and Responsibilities section of the American Bar Association. He had been an adjunct professor of law at GWU from 1982 to 1986, and he was deputy director of the science, space and technology cluster of the 1992 Clinton-Gore transition team.

Survivors include his wife, Barbara Plesser of Washington; two children, Jeremy Plesser of Clinton, N.Y., and Michelle Plesser of Bonners Ferry, Idaho; his mother, Eunice Plesser of Rockville; a brother, Andrew Plesser of Great Neck, N.Y.; and a sister, Lori Brennen of Spotsylvania.