WASHINGTON - Thanks to congressional inaction, NASA must continue to fund its defunct Ares 1 rocket program until March - a requirement that will cost the agency nearly $500 million at a time when it is struggling with the expensive task of replacing the space shuttle.

About one-third of that money - $165 million - will go to Alliant Techsystems, or ATK, which has a $2 billion contract to build the solid-rocket first stage for the Ares 1, the rocket that was supposed to fill the shuttle's role of transporting astronauts to the International Space Station.

But under a plan signed into law in October by President Obama, there's no guarantee that the new rocket required by that plan will use solid-fuel propulsion. In fact, many in NASA say a liquid-fueled rocket would be cheaper, more powerful - and safer.

The money to ATK is part of $1.2 billion that NASA will spend on its canceled Constellation program from Oct. 1 through March. Most of the rest will go to Lockheed Martin, which is building the Orion capsule intended to take astronauts into space aboard whatever rocket NASA selects. That program was largely spared by the new NASA plan.

What's more, constraints on the agency's spending resulting from congressional budget gridlock will delay the scheduled start this year of a program to modernize aging facilities at the Kennedy Space Center to transform it into a "21st-century spaceport." It's not clear when the program will begin.

The odd scenario, in which NASA is throwing money at a canceled rocket program but can't fund a modernization one, is due to several twists in the legislative process.

At the root of the problem is a 70-word sentence inserted into the 2010 budget - by lawmakers seeking to protect Ares 1 jobs in their home states - that bars NASA from shutting down the program until Congress passed a new budget a year later.

That should have happened before the Oct. 1 start of the federal fiscal year. But Congress never passed a 2011 budget, instead voting this month to extend the 2010 budget until March - so NASA still must abide by the 2010 language.

That means NASA and its contractors must keep building Ares 1, even though Obama effectively killed it when he signed the NASA plan that canceled the Constellation moon program begun under President George W. Bush.

"It would be nice if Congress did its work," said John Logsdon, space expert at George Washington University. NASA wants "to get on carrying out a good space program."

According to NASA, the agency has been spending an average of $95 million a month on Ares 1. At that rate, it will spend about $475 million from Oct. 1 to March 4 - the period covered by the current budget extension.

The language that keeps Constellation going was inserted into the 2010 budget last year by Sen. Richard C. Shelby (R., Ala.), who sought to protect the program and Ares jobs at Marshall Space Flight Center in his home state.

His office confirmed that the language was still in effect but did not respond to e-mail seeking details.

NASA officials, however, said the Ares 1 money won't necessarily be wasted. The new space plan approved by Congress calls for construction of a new "heavy-lift" rocket that would use solid-rocket engineering - if the agency selects a similar design.

"Much of the Ares 1 work likely will be directly applicable to a heavy-lift vehicle if a shuttle-derived architecture is selected," said Michael Cabbage, a NASA spokesman.

ATK says it plans to continue work at its Utah plant.