The Interior Department, intensifying its crackdown on poaching from federal coal reserves, said yesterday it has cited three more companies for unauthorized strip mining from government reserves in Alabama and has proposed new anti-poaching rules.

The department also disclosed it has reopened its investigation of unauthorized mining by Invesco International Corp., an Atlanta-based firm that has been assessed a $2.7 million fine based on a claim that the violation was unintentional. A finding that the violation was willful could result in a larger fine, the department noted.

Possibly widespread poaching from federal coal reserves in eastern states came to light last month with disclosure of a Bureau of Land Management staff estimate that coal worth $135 million to $1 billion may have been taken illegally out of eastern reserves over the years.

In a report released yesterday, Frank Gregg, the bureau's director, acknowledged the problem is "significant" but said the staff estimate was "questionable." He said that more information is required before "realistic estimates" can be made.

The three newly cited firms are Stovall-Files Coal Co., Taylor Coal Co. and Drummond Coal Co., all in Alabama. They bring the total number of firms cited to six. Forty-one other cases are being investigated, the Interior Department said.

To prevent future poaching, Gregg said, regulations are being proposed to require companies to show they have a legal right to coal before they can get permits to mine it. Additional funds will be provided for mapping and identification, he said.