This image of the surface of Mars was taken by the rover Spirit on April 18, 2006.

NASA has no plan to turn off either of its Mars rovers because of budget cuts, it said in a statement Tuesday.

The agency said that it has rescinded an earlier letter that recommended budget cuts in the Rover program to cover the cost of a next-generation rover on the Red Planet.

The move came a day after scientists at the agency's robotics centre said they would need to hibernate one of the twin Mars robots and limit the duties of the other because their budget was being cut by $4 million US.

That announcement was based on a letter NASA sent to the Jet Propulsion Laboratory in Pasadena last week. JPL manages the rovers.

But the statement Tuesday said that neither of the rovers will be shut down.

The original decision to stop one rover came amid belt-tightening at NASA headquarters, which is under pressure to juggle Mars exploration and projects to study the rest of the solar system.

The solar-powered rovers Spirit and Opportunity have dazzled scientists and the public with findings of geologic evidence that water once flowed at or near the surface of Mars long ago.

Both rovers were originally planned for three-month missions at a cost of $820 million US, but are now in their fourth year.

It costs NASA about $20 million US annually to keep the rovers running.

Last week's directive from NASA to cut $4 million US means Spirit would have been forced into hibernation in the coming weeks, said principal investigator Steve Squyres of Cornell University.

"It's very demoralizing for the team," Squyres said.

The cut comes at a time when the robots are in the midst of an extensive exploration campaign, said deputy principal investigator Ray Arvidson of Washington University in St. Louis.

"We're not done. There is still a lot to explore," Arvidson said.

The suggested cut would have forced scientists to rest Spirit, and reduce exploration by Opportunity.

"Any cut at any time when these rovers are healthy would be bad timing," Callas said. "These rovers are still viable capable vehicles in very good health."