Federal agencies have proposed designating Atlantic salmon in the Penobscot, Kennebec and Androscoggin rivers as endangered species, raising the possibility of another battle between U.S. and state officials over the beloved sportfish.

Eight years ago, federal officials added Atlantic salmon populations in more than a half-dozen smaller midcoast and Down East rivers to the endangered species list. But the federal agencies delayed a decision on the state’s largest rivers, citing the need for more study.

The proposal to extend those protections to the Penobscot — home to the vast majority of sea-run salmon returning to U.S. waters annually — as well as the Kennebec and Androscoggin rivers was not unexpected.

Several conservation groups praised the long-awaited decision, which was based on a 2006 status review involving state and federal biologists. But state officials were unenthusiastic about the prospect of adding Maine’s largest rivers — all of which have dams and heavy industry — to the list of waterways with protected salmon.

An “endangered” designation could have impacts on hydroelectric dams, large-scale water withdrawals and some industry in the watersheds. It also likely would eliminate the fall or spring catch-and-release salmon fishing seasons the state has held on the Penobscot annually since 2006.

Patrick Keliher, executive director of the state’s Bureau of Sea-Run Fisheries and Habitat, said staff would have to spend the next month digesting the recommendation before deciding how to proceed. The state went to court in an attempt to block the previous endangered designation in 2000 but eventually dropped the lawsuit.

“We’re going to weigh all of our options,” Keliher said, “but our goal is to find a way to work through the Endangered Species Act in a collaborative way.”

The National Marine Fisheries Service and the U.S. Fish and Wildlife Service are accepting public comments on the proposal through Dec. 2. The agencies plan to hold at least three public hearings. The dates and locations of those meetings will be announced at a later time.

Also known as “the leaper” for its ability to launch itself up waterfalls, Atlantic salmon were once so plentiful in New England rivers that people bragged you could walk across the river on the backs of spawning fish.

But salmon populations in U.S. waters were virtually eliminated because of construction of dams that blocked upstream passage, commercial fishing, siltation from log drives, and water pollution. The few wild salmon that leave Maine’s rivers as juveniles face long odds in the open ocean.

Comparatively, 2008 has been a good year for salmon, at least on the Penobscot. More than 2,000 adult fish have returned to the river to spawn so far, which is more than double the number in some years. But that is only about 10 percent of the figure experts estimate is needed for a self-sustaining population.

That’s why salmon reared at the two federal fish hatcheries — Green Lake in Ellsworth and Craig Brook in Orland — are included in the protection proposal, officials said. The wild and hatchery-reared fish were identified as genetically distinct populations needing protection.

“You really can’t separate the two,” said Mary Colligan, assistant regional administrator for protected species with the National Marine Fisheries Service. “The purpose of the hatchery is to rebuild the wild stocks.”

A draft copy of the proposal released Tuesday identified threats from dams, inadequate regulation of dams and low ocean survival of salmon as the biggest factors affecting the Gulf of Maine salmon population.

Restoration of salmon in Maine and elsewhere in New England is often a collaborative effort between state and federal biologists and conservation groups. The hallmark of this “cooperative conservation” approach is a plan to remove two dams in the Penobscot and bypass a third, thereby reopening nearly 1,000 miles of watershed habitat to salmon and other sea-run fish.

U.S. Sens. Olympia Snowe and Susan Collins cited that project Tuesday as proof that the endangered listing was unnecessary.

“These efforts have been a template for national restoration efforts and this heavy-handed decision is a setback for a historic endeavor to restore Maine’s Atlantic salmon populations,” the senators said in a joint statement.

“We will fight to ensure that the federal government understands that bureaucracy is not the answer to restoring the Atlantic salmon populations, rather continued state restorative efforts have been and will continue to be the most effective way to restore the salmon to historic levels.”

The Atlantic Salmon Federation said the proposal indicated that, while much has been done in recent years, additional steps are needed to save the last remaining U.S. salmon stocks.

John Burrows, ASF’s coordinator in Maine, pointed out that state officials and others made dire predictions about economic impacts from listing salmon in the eight midcoast and Down East rivers as endangered. Instead, the federal government has worked with industries, local communities and conservation groups to restore habitat, rebuild poorly maintained logging roads and replace culverts.

“The millions of dollars invested by the federal government in these collaborative efforts are benefiting both the local environment and local economies,” Burrows said in a statement.

The agencies have one year from today to issue a final rule, which also deals with critical habitat in the eight rivers designated in 2000. Those rivers are: Dennys, East Machias, Machias, Pleasant, Narraguagus, Ducktrap and Sheepscot, and Cove Brook, a tributary of the Penobscot.