Halley's Comet is coming back in 1986, and as plans currently stand, the United States won't be up there to watch.

It will be the only space-faring nation missing from the fray when the comet makes its rare swing around the sun in March 1986, Japan, the European Space Agency (ESA) and the Soviet Union together with France are launching spacecraft to intercept to comet.

An extraordinary behind-the scenes effort is under way among scientists from at least six countries to coordinate the observatin and possibly to get the United States to change its plans. Never in memory have scientists from different countries been so at odds as over their prelinary plans to study Halley's Comet, which flies in from the edge of the solar system once every 76 years. It was last seen in 1910.

"The way things are planned right now is not very sensible," said Dr. Jacques Blamont of the University of Paris, chief scientist of the ESA and the architect of the French plan to cooperate with the Soviet Union in the study of Halley's Comet. "Everybody who is doing something is going off on his own and the United States is doing nothing. It makes no sense."

At the very least, Blamont and colleagues from West Germany and Britain are trying to get the United States to let ESA borrow its deep-space tracking network and its deep-space navigating team at Pasadena's Jet Propulsion Laboratory to help guide ESA's "Giotto" spacecraft as close as possible to the comet. Blamont is also negotiationg with the Soviets to get them to aid in the navigation of Giotto (named for the 14th century Florentine artist who painted comets) by supplying them with pictures of the comet as their spacecraft cruises ahead of Giotto toward the comet.

"The Russian spacecraft will be five days ahead of Giotto and will a French camera on board that can be used very nicely to detrmine any change in the comet's trajectory," Blamont said. "If we get the Russians' help, we can fly in much closer to the comet."

Blamont is also urging the Japanese to change the instruments they plan to carry on their Halley mission. At the moment, the Japanese plan to fly a small spacecraft carrying a photometer to study from a gread distance the huge cloud of hydrogen that surrounds every comet on its flight across the solar system.

Blamont and his European colleagues are most upset by the lack of a U.S. plan to study Halley's Comet. Not only does the United States have no plans to fly a spacecraft to observe Halley, but it also has no plans to put an instrument on Giotto or to cooperate with the Soviet Union, France of the Europeans to aid their osbservations of Halley.

"We need American help, we need their superb navigating capability and their tracking antenna in Austrailia," Blamont said. "The comet is going to have a very low declination and will not be easy to observe in the northern hemisphere. The DSN [Deep Space Network] station in Australia is very, very important to this mission."

American space scientists are even more concerned than Blamont about the lack of U.S. plans. Twice in the last five years, the National Aeronautics and Administration was given plans to fly to Halley's Comet. NASA turned down the first plan because it was too expensive. The second time, President Carter rejected the scheme for the same reason.

"We have a third plan that's ready and that would do the job for $250 million," Dr. Bruce Murray, director of the Jet Propulsion Laboratory, said in an interview. "This mission would do three very important things that no other spacecraft of any other country would do because they don't have the technical capbaility. This mission is still an option for the United States."

Murry said a Voyager class spacecraft of the kind that just flew by Saturn would get superb pictures of the comet, would fly close enough in front of the comet to study the way the head of the comet boils off and determine the composition of the material boiling off.

"The Russians and Japanese will be too far away [the Soviets will never get closer than 10,000 kilometers] and the Europeans are flying a spinning [for stabilization] spacecraft," Murray said. "You can't take good pictures or get good measurements with a spinner because your exposure times are too short."

If the Reagan administration rejects the Halley plan, Murray said he will do everything he can to offer U.S. help to the other countries planning Halley missions.

"I personally have very great difficulty sitting back in the bleachers when I know we can be in the front-row seats," Murray said. "But if the decision is made not to go to Halley, I'll help htis country negotiate a junior partner role with anybody who's interested."