A firebomb thrown through a window into the Justice Department building over the weekend charred and burned documents in an office of a unit that is seeking to prosecute violators of federal hazardous waste and toxic substance statutes.

The bomb was hurled about 8 p.m. Saturday through the ground-floor window of an office facing Pennsylvania Avenue NW near the northeast corner of the Justice Department building. The fire was extinguished quickly but no inventory of documents damaged or destroyed had been made by last night.

The bombing of the office, which is used by the Justice Department's environmental crimes unit, is under investigation by the D.C. fire department, the Federal Protective Service and the FBI. Investigators said last night that they knew of no motive in the incident and had no suspects.

"On the remote possibility" the bombing was intended as a message or warning, "it must mean we are doing something right," said the head of the environmental crimes unit, Judson W. Starr.

As part of what authorities characterize as an effort to crack down on the dumping of hazardous wastes and toxic substances and other environmental violations, the unit is now involved in presenting evidence before more than 20 grand juries in more than a dozen states.

Whereas misdemeanor charges had been brought in the majority of previous attempts to curb hazardous waste violations, the unit, organized within the past two years, is seeking felony indictments, officials said.

Starr, whose unit operates under the Justice Department's land and natural resources division, said any effect of the bombing on the unit's operations would be temporary while damaged or destroyed documents are replaced.

According to D.C. fire department investigator Khalil Hassan, the bomb apparently employed a glass container to hold a flammable liquid. Witnesses said fragments of green glass believed part of the container were found inside the office on a rug near the broken window.

Fire damage was reportedly heaviest on a table beneath the windowsill of the office in which the bomb landed.

Damage caused by the fire itself was believed confined to that office, which is next to Starr's, and is used by lawyer Deborah J. Schmall.

There were indications that other offices in the suite may also have been damaged, perhaps by firefighters summoned to the scene.

One source familiar with the investigation said a photograph of a child that had apparently been kept on Starr's desk was found on the floor of his office, torn. A newspaper clipping dealing with one of the environmental unit's recent cases was also found torn.

Officials of the Federal Protective Service said they knew of no indications of a break-in connected with the bombing, and D. Jerry Rubino, director of security for the Justice Department, said the door from the corridor to the environmental unit's suite was kept locked.

He said FPS officers had checked it about one half-hour before the firebombing. When firefighters arrived, Rubino said, they broke in rather than wait for a key.

He said any disruption other than that caused by the fire apparently resulted "when the fire department got there in a hurry." He said there was no evidence anyone had been inside the suite of offices.

As of late last night, Rubino said he knew of no threats received by the environmental unit and was aware of no reason why anyone chose one of its windows as a target.

"We just don't know," he said. "It just appeared somebody threw this device at random."