ANNAPOLIS -- Imagine Maryland three hundred years ago, a comparatively untouched place where mountain lions prowled the Appalachians, bison roamed in what are now the Washington suburbs and elk could be found in every county.

If the contrast between then and now seems dramatic, state botanist Gene Cooley says that the forces that drove away the elk and other wild species are still at work today, threatening dozens of plants and less prominent critters such as the Eastern wood rat.

Whether it is the loss of habitat through development, pollution, competition with other species or long-term environmental changes such as global warming, species are disappearing within the state, some in barely a decade's time.

As a result of this extirpation, or extinction within the state's borders, Cooley and others at the Maryland Natural Heritage Program have proposed adding 281 plants and animals to the state's threatened and endangered species list. They range from the gold-banded skipper, a small butterfly whose last known habitat in the state is around the Great Falls Park area of Montgomery County, to the barking tree frog, an amphibian found in seasonally flooded ponds in some parts of the Eastern Shore.

For animals, addition to the list as an endangered species offers the protection of misdemeanor penalties against any who might harm them. For plants and less threatened animals, the protections include restrictions requiring that permits be obtained before habitat can be destroyed.

The heritage program, part of the state Department of Natural Resources, has been assembling data on Maryland flora and fauna for 11 years, drawing on historical and scientific texts, information supplied by nature hobbyists, and state-funded field surveys. The results provided a baseline for comprehensive county surveys, beginning in 1985 with counties around the Chesapeake Bay and continuing more recently with Western Maryland and the Washington suburbs.

The result is a list -- totaling 728 species with the most recent additions -- of plants and animals that are either lost in the state, endangered, threatened or in need of conservation. Almost 500 are plant species.

Extirpation doesn't necessarily mean the species is lost to the world, although in some cases Maryland harbors some of the best remaining groups of plants and animals whose existence is threatened. But each species that disappears locally, Cooley said, is a subtle injury to the state's environment.

The average citizen may never come in contact with Agalinis acuta sandplain gerardia, a purple flower endangered nationally that grows most abundantly in Baltimore County. But Cooley said naturalists view the loss of any species as a warning sign, much like the one that canaries provided to miners underground. The miners couldn't always tell what was wrong when the birds stopped singing, but they knew they were in danger.

"We don't know why they are declining," Cooley said. "But possibly these species have declined drastically because something is terribly wrong. And what is wrong could be dangerous to us."

Consider the case of the regal fritillary, a large butterfly that, at the start of the 1980s, roamed Maryland by the thousands.

For no obvious reason, its population has dwindled to as few as five, Cooley said. This spring, when the mature adult should break from its chrysalis, may mark the species' passing in this state, he said.

Another example near Maryland: within the District of Columbia, in a spring off Rock Creek, can be found the only examples left in the world of the Hays Spring amphipod, a quarter-inch long crustacean Cooley likened to a sand flea.