So tiny and strange is Pluto, smaller than Earth's moon and weirdly rotating as if lying down, some scientists have questioned its long-held status as the ninth planet.

Now, after years of on-and-off effort, the National Aeronautics and Space Administration announced last week that it has received preliminary funding from Congress for a mission to fling a spacecraft 3 billion miles or so to go take a look.

The pioneering voyage is to take about 10 years.

"It's marvelous," said Andrew F. Cheng, 50, the mission's project scientist, of the Johns Hopkins University Applied Physics Laboratory in Laurel. "It's about the most exciting thing that we've done in a long, long time."

The "New Horizons" mission, which would be managed by the Applied Physics Lab, also calls for the spacecraft to plunge beyond Pluto, into the recently discovered and even more remote Kuiper Belt.

There, some scientists believe, resides the frozen refuse of the solar system's creation, which may include fledgling comets and weird "planetoids" as big as, or perhaps bigger than, Pluto.

But it is the legendary outer planet that is the prize -- glimpsed through telescopes as a shadowy golden orb -- still one of the solar system's great secrets, 71 years after its discovery by an astronomer who was once a Kansas farm boy.

"This has been something we've worked on for 10 years," said S. Alan Stern, 44, the mission's lead investigator and director of the Southwest Research Institute's Department of Space Studies in Boulder, Colo.

"When I started, I was 30 years old," he said. "This will be my life's work. This is my contribution. It's so gratifying that we're finally going to get to do this."

NASA said Congress provided $30 million for the next phase of study and development by the Applied Physics Lab -- where the spacecraft is to be built -- the Boulder institute and other agencies on the project. NASA said further work on the $488 million enterprise is contingent on, among other things, continued funding from Congress.

But Stern vowed that the mission could be done successfully. "I know we know how to do it," he said Thursday. "We've been given the keys, at least temporarily. I can promise we're going to do as good a job as one can do in this present fiscal year to show that this is entirely doable, and on time and on budget."

The team has a key advantage: the blessing and participation of Patsy Tombaugh, the widow of Clyde W. Tombaugh, who in February 1930, at age 24, discovered Pluto.

"I wish you luck," she recently wrote the lab, "and look forward to a successful partnership in this project." Clyde Tombaugh died in 1997 at age 90.

The 1,000-pound New Horizons spacecraft, according to the plan, would be launched from Cape Canaveral atop a powerful rocket in January 2006 and hurtle into space at about 70,000 mph. "We're going like a bat out of hell," Stern said.

The first leg of the trip, dubbed "Cruise 1," would take it to Jupiter, which it would reach in about 14 months.

Plans call for it to study the giant gas planet and perhaps one of its moons and then, using Jupiter's gravity as a booster, dash into "Cruise 2," the almost decade-long journey to Pluto. For much of that time the spacecraft, with its onboard nuclear power source, would be in hibernation, physics lab scientists said, being awakened for only about 50 days each year until it neared Pluto.

Back on Earth, the New Horizons team would stand down for much of the time. Some may retire, or even "expire," as Mission Director Robert W. Farquhar, 69, of the physics lab, joked Thursday.

"I'll be 65 when we get out there," Cheng said, "but hope to be going strong. I don't plan to retire then."

"It takes a long time," he said. "The solar system's a big place. We have no choice. Laws of physics. No getting around it. We don't have a magical means to get us out there."

Stern, who will then be 58, said: "I'm looking forward to it. It gives me a reason to look forward to aging."

For Pluto, though, a decade is a trifle, a mere fraction of an orbit so vast that the planet still has not completed the 248.5-year circuit it began when Benjamin Franklin flew kites in Philadelphia.

Pluto is so small and distant that it is now generally described as a "Kuiper Belt object," associated with the huge realm of recently discovered miniature planets or ice dwarfs that float beyond its orbit. Pluto and its comparatively large moon, Charon, named for the figure in classical mythology who ferried the dead over the river Styx, "are sort of the king and queen of the Kuiper Belt," said Cheng, of the Laurel lab.

Some experts believe that Pluto no longer qualifies as a planet. Two years ago, New York's American Museum of Natural History opened an Earth and space center that excluded Pluto as a planet and listed a solar system family of just eight.

Uproar ensued.

"It is a silly debate," Cheng said. "We call it a planet. It's always been a planet, since it was discovered. Let's not waste time."

Stern, of the Southwest Research Institute, said: "If it walks like a duck, et cetera, it's a duck."

"It is true," Cheng added, "that Pluto is different."

For one thing, its mostly nitrogen atmosphere freezes and undergoes "collapse" as the planet enters its decades-long winter.

With the sun only a bright star in the blackness, the surface temperature falls to 400 degrees below zero. Fierce weather may erupt, scientists theorize, with winds that blow nitrogen blizzards at near supersonic speeds.

It is urgent that the spacecraft reach the planet before its atmosphere starts to vanish about 2020. "If we miss this atmosphere," Stern said, for "two centuries, it's very likely that there will be no atmosphere to study, or only the faintest remnants."

As the spacecraft neared Pluto and Charon, it would target the two with an array of cameras and sensors. Data and pictures should begin pouring back months before the craft makes its closest pass, 6,000 miles from Pluto, between 2016 and 2018.

When that happens, Stern said, "it'll just be breathtaking. We will, at closest approach, see objects the size of office buildings."

Back on Earth, if all goes well, aging scientists may be permitted a high-five or two, if they're still up to it.

"For all time," Stern said, "as long as we have a thread of civilization and history, the first exploration of Pluto and the Kuiper Belt will always be the pioneering mission to the frontier. It's awe-inspiring."