Opponents of bear hunting in Maryland said they plan to file a lawsuit today aimed at stopping the state's first bear season in 51 years, which is scheduled to begin late next month.

The hunting opponents said yesterday that their suit will allege that the state Department of Natural Resources did not do enough research on the black bear population -- estimated at 500 -- before determining that 30 animals could be killed by hunters.

"They should essentially have to do their homework before rushing to judgment and deciding that bears have to be killed for trophies," said Michael Markarian, president of the Silver Spring-based Fund for Animals. The suit names as plaintiffs the fund, the Humane Society of the United States and three Maryland residents, he said.

Heather Lynch, a spokeswoman for the department, said yesterday that the agency would not comment. In the past, state scientists have defended their estimates of the bear population and said a hunt is the best way to control a bear population that threatens to spread into more populated counties in the state's eastern half.

The lawsuit, to be filed in Prince George's County Circuit Court, would represent the first legal challenge in a dispute that has bubbled for years in Maryland.

The state banned bear hunting in the 1950s when only about a dozen bears were counted. But the animals have come back in Maryland and across the East Coast, helped by limited hunting and forest re-growth. State biologists, reacting to an increase in complaints about bears raiding cornfields and trash cans, this spring proposed a new hunting season.

That season is set to last from Oct. 25 to 30 and Dec. 6 to 11, with all hunting confined to Garrett and Allegany counties in the state's western panhandle. Two hundred hunters were chosen by lottery last week to receive bear permits. The hunt will be stopped after 30 bears are killed, according to state officials.

Those plans have met opposition from animal rights groups. There have been protests, an emotional legislative hearing and a barrage of calls and letters -- which state officials say have included death threats.

The state's bear population estimates were only guesswork, Markarian said, adding that they did not satisfy the state's requirements that "due regard" be given to studying an animal's population before a hunt. "It's not even close to enough," he said yesterday.