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WASHINGTON — The on-again, off-again mission to faraway Pluto may be a go if NASA can do it on the cheap and without imposing long delays on a planned exploration of one of Jupiter’s moons. 

Ed Weiler, the chief of space science, announced Wednesday that the agency was seeking proposals that would make it possible to send a robot craft to Pluto before the most distant of solar system planets sweeps out of reach. 

A launch planned in 2004 to Pluto, the only planet not yet visited by a robot probe, was  

canceled in June when costs  

spiraled. 

Weiler said at the time that rising expenses for the Pluto-Kuiper Express were threatening the schedule for a higher-priority mission: sending a probe to Europa, a Jupiter moon that may harbor an ocean and possibly life. 

The costs of the Europa and Pluto missions had risen from $650 million to $1.5 billion, said Weiler, who acted to stay within budget and preserve the Europa mission. 

The decision prompted protests from space-oriented organizations such as the Planetary Society and the American Astronomical Society. 

Planetary scientists were concerned that the opportunity to explore Pluto would be lost for years. Reaching Pluto with current technology requires a spacecraft to first pass by Jupiter, picking up speed with a gravitational boost.  

After 2006, Pluto will move out of alignment for such a boost from Jupiter and the opportunity for a Pluto mission could be lost for about 20 years. 

Under the new plan, the National Aeronautics and Space Administration is soliciting proposals for a cheaper Pluto mission that would have only a modest impact on the Europa mission launch plans. A delay of the Europa mission to 2008 would be acceptable, Weiler said, but not much beyond that. The Europa mission has a high interest and support because early studies suggests that the Jovian moon has an ice-capped ocean.  

Some scientists believe that if this is true, then there is a possibility life may exist there.  

The search for life beyond the Earth is one of NASA’s highest priorities.  

Weiler said NASA will accept Pluto mission proposals from any organization, including universities, aerospace companies and even NASA centers, such as the Jet Propulsion Laboratory, which was in charge of the canceled Pluto mission. 

“We’ll leave it to the best minds in the country to determine the mission,” he said. “We are trying to cast the net wide to see what ideas are out there.” 

Weiler said NASA is open to considering any “viable option” but is not committed to a Pluto mission. 

At least two of the proposals, which are due March 19, will be picked in May for more study. If NASA concludes a Pluto mission is possible, the announcement will be made next fall, Weiler said. 

The proposals require that a spacecraft, with specific scientific and imaging capabilities, reach Pluto by 2015 and cost no more than $500 million. 

“We are gratified that NASA is trying to restore the Pluto mission to its launch schedule,” Louis Friedman, director of the Planetary Society, said in a statement. 

He said both the Europa and Pluto missions are “essential steps in exploring our planetary environment” and NASA “must find a way to launch missions to both worlds in the next eight years.” 

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On the Net: 

Pluto-Kuiper Express site: http://www.jpl.nasa.gov/ice—fire//pkexprss.htm 

Europa Orbiter site: http://www.jpl.nasa.gov/ice—fire//europao.htm