Europe's Giotto spacecraft, carrying a dust shield designed in the United States, is on its way to a historic encounter with Halley's Comet. Just ahead of it, the Soviet Union's Vega spacecrafts are being navigated toward the comet, with a flight plan drawn up in the United States and delivered to the Soviets by a French scientist whose work took him to both countries.

To the rear are two spacecraft built and launched by Japan, the first missions beyond Earth orbit attempted by the Japanese.

No U.S. spacecraft, however, is in sight of the fleet sent to greet Halley's Comet -- the brightest comet in the heavens -- now making its first swing by Earth since 1910 and 30th recorded visit since 240 B.C.

The United States has no mission and, for the first time in memory, finds itself a spectator at a major event in space. Further, the Japanese, European and Soviet participants might not be involved were it not for U.S. help. The only active U.S. role is as navigator, using its worldwide Deep Space Network to guide the spacecraft to the comet.

"What bothers me most is the Russian mission, which used the gravity of Venus to boost their two Vega spacecraft toward the comet," said one U.S. source who asked not to be identified. "The Russians had never flown a gravity-assist mission before, and I don't believe for a minute they had the capability to fly one until we plotted the program for them to do it."

A shortage of money is often blamed for why the United States is not cruising to Halley's Comet. So is a lack of determination or imagination. But, in fact, the United States has no mission to Halley's Comet because of a combination of overexpectations, missed signals, poor planning, a streak of bad luck and politics and infighting in the science community.

The lack of a U.S. comet mission has enraged and embittered many space scientists in the United States, who now think that the U.S. leadership role in space exploration is threatened for the first time in 20 years. They fear that it is the beginning of a trend, where the United States lets Europe and the Soviet Union take on the most ambitious missions. Donald Brownlee of the University of Washington said the lack of a U.S. mission "is a disaster for American space science."

Before he was indicted on fraud charges early in December, then-NASA Administrator James M. Beggs worried that this might happen. "Sooner or later we might have to accept the fact that we can't do everything," he said. "Maybe this is the way we're going to experience life from here on out."

The story of why the United States has no Halley mission covers years, three presidents and eight federal budgets. It includes the resignations of three U.S. space officials, the untimely death of another one in the mountains of Nepal and confusion in the Office of Management and Budget.

It began in 1974. A handful of space scientists suggested the United States consider flying a spacecraft by Halley's Comet at 125,000 mph, an idea that appalled the scientific establishment. Said the Space Science Board of the National Academy of Sciences: "A Halley flyby would attact great public interest but involves such high encounter velocities as to be of very low scientific potential."

Two years later, Bruce C. Murray took over as director of California's Jet Propulsion Laboratory, where most of America's plans to explore the planets are hatched. At the time, the lab was flush with the success of the Viking program that landed two spacecraft on Mars and left two others in orbit around the Red Planet.

To keep the nation's planetary program as fresh as possible, Murray appointed committees to study the most ambitious space exploration missions possible. He said there were two kinds of mission lab could do: "purple pigeons or gray mice." A purple pigeon had pizazz, a gray mouse had none. A purple pigeon would be a rendezvous with an asteroid, a gray mouse a journey around the hot, lifeless planet Mercury.

One of the most colorful purple pigeons was a plan to use a "solar sail" to rendezvous with Halley's Comet and fly formation with it on its closest approach to the sun. The idea excited scientists because it meant a spacecraft could spend months instead of hours observing the comet.

A solar sail was described as a pair of giant wings almost a mile across using the sun's light to push a spacecraft around that part of the solar system nearest the sun. So enthusiastic was lab over the idea that its scientists and engineers wore buttons that said, "I'm a Solar Sailor."

Cornell University's Carl Sagan appeared on Johnny Carson's "Tonight" show with a vivid description of how the solar sail would get the craft to Halley's Comet without burning any chemical fuel to get there.

Looking back, many scientists say they think that the solar sail was more a purple turkey than a purple pigeon.

One Jet Propulsion Laboratory scientist said, "I think at the start everybody thought they could pull off the solar sail, but I know a lot of people are breathing easier around here that we never got the money for it."

By the time scientists worked up a flight path to the comet, it was apparent the solar sail was not the way to get there.

Any spacecraft fitted with a solar sail would have to be brought close to the sun and kept in orbit there for almost a year to let the sails soak up light.

But close to the sun, the sails would absorb more heat than light, which could melt them before the flight to the comet got under way. The alternative was to fly with sails measuring three miles across on each side so the spacecraft could remain a prudent distance from the sun. One propulsion lab engineer said, "There was no way to predict the dynamics of this sail. It was so flimsy it could end up with oscillations that would make the whole thing uncontrollable. It was an idea far ahead of its time."

There was a second option in planning a rendezvous with the comet. For years, the lab had worked on traveling long distances in space using electric propulsion. An electric-drive engine would use much smaller solar wings to change sunlight into electricity to heat a gas of mercury or cesium that could be driven out of a spacecraft's rocket engine.

Not as efficient as a solar sail, it still would get 10 times as many "miles to the gallon" as the best chemical fuel. The trouble was, it was a technique suggested so many times before it was felt to be a "loser" that could not be sold to a Congress weary of hearing about it.

Cost estimates for a rendezvous quickly climbed from $400 million to $600 million. At the same time, NASA's costs for other projects with higher priority -- the Galileo mission to Jupiter and the space shuttle -- were climbing.

It was now 1979 and time was running out because a spacecraft would have to be launched in 1983 to reach the comet in time. The Jet Propulsion Laboratory announced it was giving up the Halley rendezvous mission for a less ambitious electric propulsion flight by Halley's Comet and rendezvous with a smaller, dimmer and more obscure comet, Tempel 2.

By the summer of 1980, NASA's budget woes were peaking. The maiden voyage of the space shuttle Columbia was two years behind schedule and $1 billion over cost.

The Galileo mission to Jupiter, the Space Telescope and the International Solar Polar mission to fly a German and an American spacecraft around the north and south poles of the sun were behind schedule and over cost.

At the same time, the Halley-Tempel 2 mission had some new competition for the next new start in NASA's planetary program. This was a mission to orbit Venus to map its surface with a giant radar that could see through the clouds that cover it. The Venus Orbiting Imaging Radar mission, as it was called, had the strong backing of the nation's geologists who had run the Viking program to Mars and were overseeing the spectacularly successful Voyager missions to Saturn and Jupiter.

"The geologists said, 'Here you have an intercept mission with Halley that will be over in three hours and a mission to Venus that will go on for nine months,' " one propulsion lab source said. "The geologists used that against us."

Once it was clear that the Venus mission was competing with the Halley mission, NASA's Science Advisory Council backed the former "as the next major new start," then gave lukewarm support to the latter by urging then-NASA Administrator Robert C. Frosch to "combine whatever resources are available" in the United States and Europe for a joint mission to the comets.

"I attribute all the subsequent failures to get a Halley mission back to that priority issue," one propulsion lab source said. "Our pitch should have been that Halley was a once-in-a-lifetime chance while we can go to Venus anytime."

To hear Halley advocates tell it, the propulsion lab stuck too long with the electric-drive engine just as it had stayed too long with the solar sail. The electric-drive engine had never flown and was running over cost when the fiscal 1982 budget rolled around.

The end of electric drive meant the end of Halley-Tempel 2.

Now desperate, the lab fell back to its last option, a no-frills flyby of Halley's Comet that put the United States head-to-head with the Europeans, who had by now decided to go to Halley with a mission of their own on the Giotto spacecraft. The way this last-ditch U.S. mission was designed, it would fly as close as it could to the comet and carry cameras superior to Giotto's to photograph Halley's nucleus.

In the midst of this turmoil came more chaos. Thomas Young resigned as NASA's planetary program director, and Frosch quit as administrator. Then, calamity struck. Thomas A. Mutch, associate administrator for space science, a mountain climber and an advocate for a Halley mission in NASA's hierarchy, was killed by an avalanche in the Himalayas. All of this happened in the fall of 1980, as NASA was readying its final budget plan for OMB review.

When the NASA budget was drafted by acting administrator Alan Lovelace, the Venus mission was in the budget but the Halley mission was not. The geologists had won, the growing numbers of comet scientists had lost. Lovelace visited OMB in December for a last session with Director James McIntyre.

"McIntyre decided if Lovelace asked for the money to go to Halley we would give it to him," said a high-ranking OMB official who asked to remain nameless. "He didn't ask so we asked him. I remember his response very well. He said, 'It's too late. I don't think we can make it.' "

Lovelace left just as the Reagan administration took over in January 1981, leaving NASA without an administrator until Beggs joined NASA in June. Beggs was visited by Jet Propulsion Laboratory Director Murray in a final effort to keep the Halley mission alive.

By then, OMB Director David A. Stockman had stretched out the Venus mission to 1988 and ended U.S. participation with Germany in the solar polar mission. Beggs said, "OMB wanted to give up planetary exploration entirely. I had tougher battles to fight than Halley."

On Sept. 1, 1981, Murray told Beggs the United States could mount a mission to Halley with a spacecraft carrying an instrument to spear a sample of the comet's dust and return it to Earth in the same way the Air Force returned spy satellite pictures. Murray even had a spare Air Force spy satellite for the mission, which he priced at $300 million.

The science community backed the sample-return mission. Even the American scientists against a flyby mission reversed themselves, including Cornell University scientist Joseph Veverka who had once called a flyby a "scientific stunt" but now said, "Our grandchildren will never forgive us" for missing the Halley opportunity.

But it was too late. Before October began, Beggs told Murray that Halley was history. Soon after, a French scientist whose instruments had flown on U.S. and Soviet missions to the planets visited the propulsion lab and asked if a Soviet spacecraft flying to Venus could proceed on to Halley's Comet.

Knowing the Frenchman might take the information back to the Soviets, the lab told him it could be done and even told him how to do it.

A month later, the Soviets announced they would send two Vega spacecraft to Venus and then on to Halley. About the same time, the propulsion lab gave the Europeans blueprints for a shield to protect the Giotto spacecraft from comet dust. And at the same time Murray resigned from the lab, telling friends he could not bear to remain if the United States had no mission to Halley.

"Do I regret it? Yes, I regret it," Beggs told The Washington Post recently. "You only get one look at Halley in a lifetime, and I think if NASA had to do it all over again we'd have our own mission."