PROVIDENCE, R.I. – The amount of adult cod in New England waters decreased in 2004 as overfishing continued, according to a report released by federal regulators on Tuesday.

Representatives of environmental groups expressed concern at the falling numbers and warned that the cod stock, a longtime staple of New England, could again be near collapse.

“Fishery management in New England has been a series of failures where New England’s world-renowned cod fishery is now at the brink of collapse due to continued overfishing,” said Chris Zeman of Oceana, an oceans advocacy group.

But a spokeswoman for the federal NOAA fisheries agency said such dire predictions were unfounded and that fishing rates were in the process of being controlled.

“I don’t see how you can draw that conclusion [of a collapse] based on this report,” said the spokeswoman, Teri Frady.

The population of cod found near Georges Bank, off New England, decreased by 25 percent since 2001, the report shows. Cod stocks in the Gulf of Maine dropped 21 percent.

The report, which follows last month’s release of preliminary stock assessment numbers, was to be discussed Thursday at the New England Fishery Management Council meeting in Providence.

Researchers updated the assessments of the health of 19 groundfish stocks that live in New England waters, including cod, halibut, haddock and flounder.

Frady said while the populations may have gone down in both cod stocks, the fishing rates for the Georges Banks cod declined by 50 percent since 2001. She said the decrease was encouraging and an important step toward rebuilding that stock, a process expected to take several years.

“There’s less fishing and that’s something you have to have if you’re going to rebuild those stocks,” Frady said.

The report shows that the rate of fish caught declined for 13 of 19 stocks between 2001 and 2004. Six other stocks, including Georges Bank haddock and Atlantic halibut, experienced increases, according to the report.

The government in May 2004 implemented strict new fishing regulations known as Amendment 13. Russell Sherman, a fisherman in Gloucester, Mass., said not enough time has passed to assess if the new regulations are helping the fish stocks.

“When is somebody going to give these regulations a little time? That’s what I want to know,” Sherman said Tuesday. “This is the age of instant gratification.”

But environmentalists said they were troubled with the report’s findings, saying overfishing was continuing in New England waters and that fish are being caught at too high a rate to sustain their populations.