WASHINGTON (AP) _ A $10 billion international fusion energy project won't work, a new theory indicates, but a government official said the design can be changed if the theory is proved.

Researchers at the University of Texas and Princeton say they have computer models showing the current design of the International Thermonuclear Experimental Reactor, or ITER, will not produce the fusion energy reaction its designers expect.

``Our studies suggest that a different design would be more successful and substantially cheaper,'' said William Dorland, a University of Texas physicist. Furthermore, he said, ``our calculations do indicate that the current design would fall far short of expectation.''

The reactor is a building-sized machine planned to demonstrate that the power of the sun _ nuclear fusion _ can be created and controlled long enough to become useful in producing energy.

Current atomic power plants are based on fission, in which atoms are split to release energy. Atomic fusion energy would come from forcing atoms to fuse together to emit heat, helium and only a modest amount of radiation.

The project as now planned is a 52-foot, doughnut-shaped machine called a Tokamak. It is designed to achieve fusion by heating ionized atoms of deuterium and tritium, two forms of hydrogen, to millions of degrees as they are compressed by magnetic fields.

If it worked, a self-sustained nuclear burn would occur, giving off more energy than it would take to ignite it.

Physicists Dorland and Michael Kotschenreuther of the University of Texas and Mike Beer and Gregory W. Hammett of Princeton University say a new understanding about the turbulence and heat flow of the atoms inside the Tokamak suggest the current design will fail.

Dorland said the main problem is that the current design would permit too much heat to escape for the atoms to usefully reach the fusion flash point.

``Our theory is new and controversial, but there is a lot of support in the fusion community,'' said Hammett. He said scientists in the reactor project ``are considering the issues that we raised.''

The journal Science, which disclosed the controversy, said some members of the project team expressed anxiety about the Texas-Princeton theory.

Marshall Rosenbluth of the University of California, San Diego, and a team member, said in Science that the Texas-Princeton work is ``a remarkable intellectual achievement.''

``I don't think this theory is a basis for changing the ITER design at this point or for causing the work to come to a halt,'' said Anne Davies, director of the Department of Energy's office of fusion energy and the project's top government figure. ``The fusion community doesn't consider it a complete product as yet.''

Dorland and his colleagues have presented the findings at several scientific meetings over the last year.

``There is not yet a consensus from the fusion community that we are correct, but the work is much respected,'' said Dorland.

Davies said project scientists will examine and evaluate the Texas-Princeton theory before a final design is drawn up in March.

``It will be considered,'' she said, but it is too early to tell if the final design will include the Texas-Princeton findings.