SPRINGFIELD, Mass. (AP) _ Rappelling down the side of a 23-story building to save an unhatched peregrine falcon egg was ''absolutely worth it,'' even though the egg proved to be infertile, a state preservationist said Thursday.

''There are so few peregrines left we had to try,'' said Thomas French, the head of the state's endangered species program.

French, who donned a hard hat and gauntlets to protect himself from the diving attacks of the parent birds, said he actually felt more comfortable inching down the office building Wednesday than he has climbing some high cliffs to band young ravens.

''I had so much gear on I was perfectly safe,'' he said. ''It's really all in the mind.''

''The adults popped me a few times on the head and the hand as I was going down, and once on my boot as I was sitting on the ledge,'' French said. ''But mostly all I could feel was the whoosh of wings and the wind as they passed.''

He estimated that the adults, which can reach speeds of 185 mph, dived at him at speeds of about 60 mph to 70 mph even in the tight quarters.

French sent the egg up to the roof in a can. But after taking it to his Conway home in hopes of incubating it, Thomas P. Ricardi, a master falconer, said it contained no embryo.

''My heart kind of sank,'' Ricardi said.

Two other eggs in the nest on a ledge at the 21st floor had already hatched, the first to do so here in more than 40 years.

If the remaining egg could have been hatched, the chick would have been returned to the nest under a state program to preserve the species, he said.

Falcons, swift predators that had all but disappeared from the East Coast because of damage by the now-banned pesticide DDT, are begining to make a comeback after more than a decade of private and governmental efforts in the United States and Canada, French said.

''In 1966 there were no breeding pairs left in the East, except in northern Canada,'' he said. ''Now we have 80 breeding pairs and we've reached a turning point where we have more breeding pairs in the wild than in captivity.''

Since 1974, the private Peregrine Fund has raised more than 1,000 birds for release in both urban and rural areas, he said.

Although they normally nest on high cliffs, peregrines have taken a liking to the high ledges of city skyscrapers where they can indulge their taste for pigeons.

Massachusetts released young falcons in Boston and Amherst. But the Springfield pair, including a female released in Toronto as part of the Canadian government's restoration program, found this Connecticut River city on their own. The male is also banded, but officials haven't yet determined his origin.