PORTLAND – Cod and haddock are once again filling fishermen’s nets from Maine to Rhode Island, but the rebound of groundfish stocks isn’t all good news.

It’s creating a dilemma for fishermen and resource managers: How to keep hundreds of boats with valid fishing permits from returning to the fishery and undoing years of painful conservation.

The federal government is so concerned it’s about to offer $10 million to buy groundfishing permits that may have been unused for years. And fisheries managers are considering freezing or limiting new fishing permits.

Doing nothing could leave the door open for the fleet to grow out of control again. And that would mean a return to overfishing, and a new round of restrictions that could wipe out the fleet of year-round fishing boats that tie up in ports in Maine and other New England states.

Taking away the traditional ability of Maine’s scattered small-boat fleet to switch from lobster or scallop fishing back to groundfish could threaten island and coastal communities that those fishermen support.

“What happens if lobster starts to founder – and we’re seeing signs,” said Willis Spear, a fisherman from Cousins Island off Portland. “If [fishermen] don’t have flexibility, it’s going to ruin the coastal communities.”

A buildup of the New England groundfish fleet in the 1980s, combined with improved fishing technologies, led to the collapse in the 1990s of fish such as haddock on Georges Bank and cod in the Gulf of Maine.

That prompted the federal government to buy dozens of fishing boats as a way to lower catches and ease pressure on groundfish.

The crash sent many fishermen to another fishery, notably lobsters, which provided them with suitable pay. But the fishermen kept renewing their groundfish permits, knowing they might need them in the future.

The National Marine Fisheries Service plans to offer $10 million to buy out permits. It’s unknown how many permits the money will buy, but there’s little expectation the problem will go away entirely.

Later this month, members of the New England Fishery Management Council will consider nine proposals to control the rebuilding of the groundfish fleet.

The proposals include such ideas as freezing unused permits and cutting a percentage of the fishing days on permits. Some call for the council to revoke permits that have not been used, but that outcome is unlikely, said Douglas Hopkins, a lawyer for the Environmental Defense Fund who heads a council committee studying the options.