The White House has quickly reversed itself on a major environmental problem and embraced the idea of a formal treaty-negotiating process on global warming.

The decision puts the United States in line with all other major Western economies in supporting such an initiative.And the reversal occurs the same week a government scientist testified that the White House made him alter his testimony on the "greenhouse effect" to give the impression that not everyone agreed on the severity of the problem.

The change of course was revealed in a cable dispatched Thursday night to U.S. delegates at an environmental conference in Geneva sponsored by the United Nations.

Declaring it was essential for the United States to exercise a leadership role, the cable said, "We should seek to develop full international consensus on necessary steps to prepare for a formal treaty-negotiating process."

It proposed that U.S. delegates seek agreement for a "global warming workshop" hosted this fall by the United States.

The cable, a copy of which was obtained by The Associated Press, was signed by White House chief of staff John Sununu, who only last week had rejected efforts to put the United States in the lead in establishing an international convention on global warming.

The convention idea had been supported by Secretary of State James A. Baker III and Environmental Protection Agency Administrator William K. Reilly.

Scientists believe that global temperatures could rise by 4 degrees or as much as 9 degrees Fahrenheit by the middle of the next century because increasing levels of carbon dioxide and other manmade gases in the atmosphere will trap and retain heat from the sun in a process similar to what happens in a greenhouse.

Such a warming trend could melt polar ice caps and cause sea levels to rise, cause severe droughts and storms and severely disrupt the Earth's biological systems.

Scientists at a Senate hearing on Monday testified that the problem might be worse than their own computer programs can predict.

The White House had ordered one of the scientists, James E. Hansen, director of National Aeronautics and Space Administration's Goddard Institute for Space Studies, to change his testimony to avoid the impression "that there is unanimity within the government on this issue."