WASHINGTON — NASA advocates expecting a big boost to the U.S. space agency’s budget in 2011 are likely to be disappointed when the administration of President Barack Obama delivers its annual funding request to lawmakers Feb. 1, according to sources with close ties to the administration.

NASA’s budget, just over $18.7 billion this year, is still expected to rise  again in 2011, these sources said, but by much less than the $1 billion increase NASA and its contractors have been privately anticipating since mid-December,  when Obama met with NASA Administrator Charles Bolden to discuss the findings of a White House-appointed panel tasked with assessing alternatives to the agency’s Constellation program, a five-year-old effort to replace the space shuttle with rockets and spacecraft optimized for the Moon. The panel, led by former Lockheed Martin chief Norm Augustine, urged the administration to consider abandoning parts of that plan and relying on the private sector to transport astronauts to the international space station. In addition, the panel called for a gradual increase in NASA spending over the next four years, beginning with about $1 billion in 2011 and ramping up to a roughly $3 billion annual increase over 2010 projections by 2014.

Although Obama’s 2011 budget request is no longer expected to include the $1 billion boost that has undergirded NASA’s planning in recent weeks, sources familiar with the latest developments said any increase is an improvement over NASA spending projections Obama sent to Congress last year.

Those projections showed NASA’s 2011 budget declining by 0.3 percent relative to $18.68 billion Obama requested for the agency for 2010. Sources said NASA instead will see a slight increase, despite Obama’s November guidance to federal agencies to plan for a freeze or even a five percent cut to their budgets in 2011.