WASHINGTON (AP) _ Deadly gas and flooding continue to pose a threat at Lake Nios in the African nation of Cameroon, where more than 1,700 people were killed by a gas cloud last summer, American scientists said Wednesday in proposing actions to ease the danger.

A series of steps, including lowering the level of Lake Nios and removing dissolved gas from the lake, were recommended in the final report of the American scientific team.

An unstable spillway on the lake poses a threat of major flooding in the area, Dr. Edward J. Koenigsberg, of the U.S. Office of Foreign Disaster Assistance, warned at a State Department briefing.

And the water in the lake still contains high concentrations of dissolved carbon dioxide, raising the possibility of another sudden gas cloud similar to the one that claimed 1,746 lives last Aug. 21, he added.

Those victims were smothered by a cloud of carbon dioxide that bubbled out of the lake, the study concluded.

The U.S. team will return to Cameroon next month to meet with local officials and scientists from several other nations to compare findings and proposals for preventing further tragedies, Koenigsberg reported.

While investigatiors have concluded that the carbon dioxide cloud killed the vicitims of the disaster, the mechanism that caused it to burst forth from the lake remains in some dispute, Koenigsberg said.

American scientists believe the gas, which originated in molton rock deep in the earth, was dissolved in the bottom layers of the lake and suddenly bubbled forth, the way carbon dioxide bubbles out of a soft drink when the cap is removed.

The trigger could have been a storm above the lake, a small landslide, runoff from heavy rains at the time or even seasonal cooling, Koenigsberg said.

Normally, water in lakes like Nios remains very stable, allowing gas concentrations to build up. By contrast lakes in cooler climates such as the United States have a regular circulation because of seasonal warming and cooling, and that prevents such a buildup.

Carbon dioxide is invisible and generally considered odorless and tasteless. It can be formed from natural chemical reactions, which is usually how it gets in beer and sparkling wine, where it forms the bubbles.

It can also originate from molton rock, and the lava underlying volcanoes in Cameroon appears to contain large amounts.

French scientists have a different theory of the cause of the disaster, contending that a huge bubble of gas from deep in the earth suddenly burst through the lake.

While the cause remains in dispute, Koenigsberg suggested that a major problem continues at a spillway on the lake. Formed of soft, volcanic rock, the spillway is leaking and could collapse, he said, posing a danger of serious floods. A collapse could drop the level of the mile-square lake as much as 120 feet, he said.

Koenigsberg proposed slowly lowering the lake level and then demolishing the spillway, after temporarily relocating area residents.

As to the gas trapped in the lake waters, he said U.S. Environmental Protection Agency officials have proposed a system of deep tubes which could siphon water from the bottom to the surface, allowing carbon dioxide to bubble out gradually. This would take about three years, he said.

In addition, Koenigsberg said scientists should launch a study of other area lakes to determine if any contain large concentrations of carbon dioxide.

A gas release at Lake Monoun, about 100 miles from Lake Nios, killed 37 people in 1984, he noted, and there are 40 or more lakes in the region located in old volcanic craters, similar to Nios and Monoun.

While the tragedies in 1984 and 1986 have thrust the problem into the worldwide spotlight, stories of exploding lakes have been part of the folklore of the region for centuries.

Residents of the area refer to some lakes as good lakes and others as bad lakes. Until last August, Koenigsberg said, Nios had been thought of as a good lake.