Interstate Commerce Commission decisions commonly are leaked to interested parties before they are made public, a Justice Department lawyer said this week.

Stephen H. Lachter, an antitrust division attorney, said he knows of three such instances and has been told by Justice lawyers of others.

"Leaking of information is common-place," Lachter said. "It indicates a course of conduct that opens up questions about their decision-making process."

Lachter said he was acting as a lawyer who deals with the ICC rather than as a Justice spokesman.

He said he knows of no connection between the leaks and a current Justice investigation into possibly improper contacts between ICC officials and trucking companies with suspected ties to organized crime.

Justice sources say the trucking investigation, headed by John Dowd, centers in part on whether advance word of ICC decisions was leaked to interested parties or organizations. Two ICC officials, Robert L. Oswald and Richard W. Kyle, have been placed on administrative leave pending the outcome of the investigation.

This week, a third ICC employee, Patricia Brislin, was placed in administrative leave pending the outcome of a Civil Service Commission investigation of her employment in light of her indictment in Los Angeles June 9.

Brislin and Stephen Elko, a former administrative assistant to Rep. Daniel J. Flood (D-Pa.), were charged with conspiring to obtain bribes for Los Angeles vocational schools to make them eligible for federal funds.

Two of the instances of leaks cited by Lachter formed the basis of complaints to the ICC by Washington lawyer Allan I. Mendelsohn, who represents shippers.

In letters sent to the ICC within the past several months, Mendelsohn charged that decisions on applications to carry meat to the East Coast had been imparted in ex parte contacts to interested persons. Such contacts, inbeen imparted in ex parte contacts to ing, are prohibited by ICC regulations.

Lachter referred to a third alleged instance in a paper filed with the ICC concerning the same case, known as Scott Truck Line, Inc.

" . . . we are disturbed by the apparent ex parte contact between counsel for Curtis (an objector in the case) and the administrative law judge," Lachter said. "Counsel's admitted conversation with Judge (Edward J.) Reidy raises questions concerning compliance with the commission's rules of conduct . . . " Reidy could not be reached for comment.

Ivan M. Schaeffer, an ICC official, said Mendelsohn's complaints had been investigated and were found to be untrue.

He said a decision in dispute was made public before interested parties became aware of it.

Lachter, informed of the ICC position, stood by his statement. "I know first hand of three instances where information was leaked before it became public," he said.

"They have a system they've developed that works well for the little in-group of motor carriers and their lawyers," Mendelsohn said. "The result is you never know when decisions will be leaked."