NEW SALEM, Mass. (AP) _ The doctor wore hiking boots and the patients got a treat of fresh-caught fish as state wildlife officials paid a cautious house call on a pair of bald eagle chicks, 55 feet up a red oak tree.

The chicks, fathered by Ross, the first eagle released in Massachusetts' 9- year-old restoration program, were due for their first - and, biologists hoped, last - medical checkup and contact with humans.

In the past three years, the program has produced five nesting pairs and 13 Massachusetts-born chicks, most at the wild, 32-square mile Quabbin Reservoir in western Massachusetts. But state wildlife officials say there is still much to be learned about the national symbol that has made a remarkable comeback across the United States since the banning of the pesticide DDT.

In a measure of how precarious their toehold remains, officials in Maine recently sought Massachusetts medical data to help determine if long-term pesticide effects were causing a decline in the fertility of their 126 breeding pairs, said Thomas French, director of Massachusetts' endangered species program.

In 1989, Ross and his mate produced two of the state's first eagle chicks in nearly a century and last year, after losing their own chick, they successfully fostered a young eaglet hatched in captivity.

It was no limousine house call last week at the 4-foot stick nest overlooking the reservoir and a stand of blooming mountain laurel.

The biologists, laden with nets, climbing gear, collecting boxes, a full veterinary medical kit, two cloth bags and a 12-foot ladder, parked their boat around a far point. Then they hiked in through the wet woods.

Upon arrival at the nest site, French and Bill Byrne, a division photographer, climbed the oak, using the ladder to get past the wire mesh wrapped around the tree to discourage beavers.

At the same time parasitologist Mark Maloney of the University of Massachusetts picked through the leaf litter below for eagle droppings.

''Some people get the glamour jobs and some just do this,'' said Maloney as he used a butter knife to scrape remnants off his hands and into a collecting box. ''Eagles go over the side to keep the nest clean.''

Among other things, Maloney searched for evidence of the liver flukes that killed the eagles' chick last year.

While the parents were away, French gently stuffed the chicks into cloth bags to lower them to the ground.

There they were weighed and had their ears, eyes and throats checked by Diane Benson, a technician with the Wildlife Clinic at Tufts University, who served as the foster mother to Ross' mate and seven other young eagles reared and released at the reservoir in 1985.

''You know, you are my grandchild,'' she told the first male chick, which at 4 1/2 weeks of age already weighed 6 pounds, 10 ounces. The dark, downy fledgling carefully watched her.

The second eaglet also was declared ''very fit'' by Benson. But as it was rebagged and raised to the nest the mother eagle appeared over the trees, carrying a fish. She let out a startled squawk when she spotted French and the fish splashed into the water.

As she circled the nest, an angry silhouette against the storm clouds, a loon sailing offshore answered her screams with its own eerie call.

The mother did not attack, but the reservoir echoed with her strident challenges as French replaced the second chick, weighing 7 pounds, 3 ounces, and quietly retreated.