Aliens wreak havoc in Hawaiian islands.

Slithering snakes snacking on endangered birds. Inflammable grasses turning timber stands into tinderboxes. Roving rabbits ravaging acres of vital vegetation.

These are but a few of the alien species under attack by Hawaii's ecologists and conservation managers.

So far, officials have the upper hand against these strangers in paradise, but a report released this week by two environmental groups warns that Hawaii's unique ecosystem may suffer irreversible damage unless state and federal practices are beefed up to stem future alien invasions.

The report -- prepared by the Nature Conservancy of Hawaii in Honolulu and the Honolulu headquarters of the Natural Resources Defense Council -- calls for Hawaii's agriculture department to take the lead in a multi-agency effort to develop better ways to keep pests from entering and eradicate them if they do arrive. Scientists discussed the report in Honolulu this week at the joint annual meeting of the American Institute of Biological Sciences and the Ecological Society of America.

Alien species "are our number-one problem," says Patrick Dunn, a stewardship ecologist with the Nature Conservancy of Hawaii. He estimates that National Park Service managers in Hawaii spend 80 percent of their time fighting alien species that threaten to disrupt the ecological balance of the islands' national parks.

Roughly 20 additional species of alien insects alone enter Hawaii each year. Some become crop pests, introduce human or animal diseases, or eat native insects important for pollinating plants. Others simply outcompete native insects for resources such as food or breeding areas.

Hawaii is particularly vulnerable to the effects of introduced species. For centuries, a new species traveled the 2,500-mile distance from the nearest land masses only once every 100,000 years. The difficult crossing left Hawaii with no native mammals save a single species of bat, and with no native snakes. Today, when such animals arrive, they have no natural predators and can multiply out of control.

Hawaii has regulations designed to bar unwanted immigrant species -- including Customs-like declaration forms for incoming domestic airline passengers -- but these have proved ineffective, according to the report. Nearly a dozen state and federal agencies have jurisdiction over some facet of alien-species introduction and control in Hawaii, resulting in "many gaps and leaks for pest entry and establishment," the report states.

Officials from various agencies have agreed to meet later this month to develop new control strategies -- such as programs for inspecting samples of arriving cargo, mail, and passengers -- and to identify changes needed in regulations. Once these are in place, the report recommends establishing computerized systems for tracking alien species, coordinating research across various agencies on the effects of introducing aliens, and expanding campaigns to publicize the dangers.

"The problem is very serious," says Yukio Kitagawa, chairman of Hawaii's agriculture department. "This report not only identifies the gaps in our alien-species control system, but it also proposes the critical steps we must take to close those gaps."