The Federal Energy Regulatory Commission is accepting comments on the proposed relicensing of four hydroelectric dams owned by Great Northern Paper Inc.

Known as the Penobscot Mills Project, the dams are part of an extensive hydroelectric system operated by Great Northern on the West Branch of the Penobscot River. The system generates electricity for the GNP mills at Millinocket and East Millinocket.

The start of the FERC review is a major step forward for Great Northern, which is seeking 30-year licenses to continue operating the system. The comment period expires May 24.

“The process is moving,” said Gordon Manuel, a spokesman for GNP. “We are optimistic that FERC will act by the end of the year.”

Although it is part of the GNP hydroelectric system, the Ripogenus Dam is being treated as a separate project by state and federal regulators.

Despite efforts by environmentalists and others to force Great Northern to change its proposals, the Penobscot Mills and Ripogenus dams are expected to receive state water-quality certifications later this month.

Daniel L. Sosland, attorney for the Conservation Law Foundation, said the environmental coalition would continue to voice its concerns at the federal level.

“We will file an extensive request to FERC on all of the major issues raised to date,” said Sosland. “There is absolutely no question that the 401s (water-quality certifications) are the result of a political process and not an analytical one.”