Researchers at Wyoming's Game and Fish Department are developing a vaccine to protect black-footed ferrets from canine distemper, the disease that nearly eliminated the endangered mammals a few years ago.

"Canine distemper seems to be a real problem," said Art Reese, the department's chief of habitat and technical services. "The problem that we have is that in canine distemper for dogs and cats, a vet will give those animals a live vaccine. You can't do that with a ferret. We tried that with the first ones and it killed them."

An epidemic of the disease nearly wiped out what was believed to be the last of the masked creatures in 1985 and prompted Game and Fish biologists to rescue them from their colony near Meeteetse, Wyo.

Since then the department's efforts at captive breeding have yielded 58 kits, six of which were sent last week to a similar breeding facility at the National Zoo in Front Royal, Va.

Another concern to biologists at the Sybille Canyon research facility is losing genetic diversity among breeding ferrets. They estimate the ferrets live about five years, and as females age they produce fewer litters.

Reported sitings of black-footed ferrets in Canada have not been verified, he added, but if any populations were found outside Wyoming the Game and Fish Department likely would seek to bring some of the animals to Sybille.

Officials hope to reintroduce 50 ferrets back to the high plains desert around Meeteetse sometime in 1991.

The following year they hope to begin reintroduction in other Western states - Montana, Colorado, Idaho, Utah and Nebraska - that are part of the ferrets' historical range.

But ferrets that have never been outside a laboratory will have to be taught to get along in the wild, so the department is building prairie dog towns to get the creatures used to their natural habitat.

While biologists see being able to expand the breeding program outside Wyoming as a great achievement, Reese added, their main goal is to set the creatures free.

"The real success story will be when they're in the wild and can live on their own," he said.