MOUNTAIN VIEW, Calif. (AP) _ The Pioneer Venus orbiter ran out of thruster propellant Saturday after circling Venus for 14 years, and is expected to plunge toward the planet this week, a NASA spokesman said.

The National Aeronautics and Space Administration learned of the orbiter's imminent demise when its thruster failed to fire, said Peter Waller, spokesman for NASA Ames Research Center in Mountain View.

''It's up and out of danger right now, but we've been firing thrusters to keep raising it and this time there wasn't any propellant,'' Waller said.

He said Pioneer would plummet through Venus' atmosphere and lose communication sometime this week. The spacecraft was expected to burn up in Venus' atmosphere.

The Pioneer Venus orbiter was the first U.S. spacecraft to circle Venus. It was expected to last only one Venusian year - 243 days.

Over the years, the 810-pound spacecraft used a crude radar to peer through the planet's thick clouds and map more than 90 percent of its surface.

The orbiter discovered that Venus has large valleys and a 7-mile-high mountain named Maxwell Montes, which is taller than Earth's Mount Everest.

Much more detailed pictures of the planet's surface have been made by NASA's Magellan spacecraft, which recently finished mapping 99 percent of the volcanic landscape.