WASHINGTON - In a sternly worded letter to acting NASA Administrator Frederick D. Gregory, Sen. Barbara Mikulski (D-Md.) said she expects the U.S. space agency to heed the will of the Congress and keep preparations for a Hubble Space Telescope servicing mission on track.

Congress, in passing an omnibus spending bill late last year, directed NASA to set aside $291 million of its 2005 budget to spend planning and preparing for a servicing mission to Hubble by 2008. When NASA informed Congress just weeks later that it intended to spend only $175 million of that amount on the Hubble repair effort, some saw the move as an indication that the agency was preparing to abandon plans to service Hubble robotically and rely instead on a space shuttle crew to fix the telescope.

Many Hubble backers, including Mikulski, were shocked and angered when NASA announced in early February that it would not make any effort to service the telescope beyond attaching a propulsion module that can be used to drop Hubble into the ocean once it goes dark.

Mikulski, an influential member of the Senate Appropriations Committee, told Gregory in her March 2 letter that Congress will consider this year including money in NASA's 2006 budget for a Hubble servicing mission. In the meantime, she said, she expects NASA to spend every penny of the $291 million included in the 2005 budget for Hubble servicing.

"I expect NASA to carry out Congress' intent and spend the entire amount appropriated this year so there will be no interruption in the planning, preparation and engineering work that will be necessary for a servicing mission to Hubble," she wrote. "The funding that I included in the Omnibus Appropriations Act is to ensure that the workforce at Goddard, the Space Telescope Science Institute and their associated contractors remain fully engaged in all aspects of a servicing mission. Any attempt to cancel, terminate or suspend servicing activity would be a violation of the law unless it has the approval of the House and Senate Appropriations Committees."

Government agencies are required to seek permission from congressional appropriators before using money for purposes other than which it was originally approved. Although the Omnibus Appropriations Act of 2005 gives NASA "unrestrained transfer authority" to move money between accounts, it also says that the authority should be used primarily to help the agency complete its transition to full-cost accounting.

NASA has not canceled contracts it awarded to Lockheed Martin and Canada's MDA Robotics last year to help engineers at Goddard Space Flight Center in Greenbelt, Md., design a robotic servicing mission. NASA officials have said the agency intends to let that work continue at least until a preliminary design review planned this month.