WASHINGTON — NASA Administrator Mike Griffin dismissed the oft-repeated criticism of recent years that science is being shortchanged to pay for human space flight, calling the claim a “political tactic” that is unsupported by facts.

“I used to think it was a legitimate concern and now I’ve gotten to the point where I think it’s a political tactic … because if it was a legitimate concern, the data would support that concern,” Griffin said in an interview that aired April 8 on C-SPAN’s Newsmakers program.

Griffin has been sparring with the NASA-funded science community since the U.S. space agency released budget projections in early 2006 that slowed the rate of growth for Earth observation, astronomy and other space sciences by about 1 percent annually while forecasting double-digit growth in spending to replace the space shuttle with spacecraft capable of going to the Moon.

Griffin’s comments on Newsmakers were some of his strongest yet and follow criticism he leveled last month at a National Research Council report calling for NASA to increase its Earth science expenditures by a third in order to keep the nation’s system of environmental satellites from collapsing. Both the House and Senate have held hearings to examine the report’s findings and recommendations. Some NASA officials fear that Congress will heed the report’s advice and put more money toward Earth science at the expense of the agency’s shuttle replacement effort.

Griffin, ostensibly seeking to head off a realignment of NASA spending priorities, emphasized during the interview a point he is fond of making: Historically speaking, the share of NASA’s budget devoted to science is near an all-time high.

Science today, he said, receives about 32 percent of NASA’s $16.2 billion budget, up from the 24 percent share it received in the early 1990s. During the Apollo era, he said, science was just 17 percent of NASA’s portfolio.

“It’s really hard for me to … see anything other than the fact science has gained enormously at NASA, and frankly I think scientists should be grateful rather than complaining,” Griffin said.

Griffin acknowledged, however, that over the next four years “the science budget will not grow as much as everybody had at one time hoped. It will grow less. NASA is growing less than we had at one time hoped.”

Since NASA embarked on the Vision for Space Exploration three years ago, the agency’s annual budget has fallen about $1.5 billion behind where it was supposed to be by now.

Rather than receiving the three consecutive years of nearly 5 percent increases the White House initially promised to pay for the exploration initiative, the agency has been struggling to keep up with inflation while paying off a $2.7 billion bill for returning the space shuttle to service following the February 2003 Columbia accident.

Compounding NASA’s fiscal difficulties, the agency was denied a budget increase for 2007 when Congress, in the interest of time, funded most non-defense agencies at last year’s levels.

“A $2.7 billion bill is real money to pay off over a few years,” Griffin said. “I don’t know what to say except that bad things do happen, but I have tried as hard as I can to see to it that unduly bad things do not happen to science as a result of things going on in the manned space flight portfolio, and the data back that up.”

According to NASA’s 2007 initial operating plan, sent to Congress in mid March for review, the space shuttle and international space station programs will command 35 percent of NASA’s budget this year, or $5.75 billion.

A further 15 percent ($2.55 billion) will go toward development of the Orion Crew Exploration Vehicle and its Ares 1 rocket, the documents show, while science is budgeted at 33 percent of NASA’s top line, or $5.37 billion. Aeronautics’ share of the total, meanwhile, is under 5 percent, or $716 million.

Griffin has pointed out over the past year that NASA’s exploration systems budget is not growing as fast as he had hoped either, prompting numerous project cancellations within that portfolio.

In hearings before Congress this spring, Griffin testified NASA will not be able to meet the 2014 deadline set by the White House for fielding Orion and Ares.

Griffin made that point again on Newsmakers, saying the new vehicles would not be ready to enter service until 2015 given current budget projections, three years later than Griffin thought possible when he took the helm of NASA in 2005.

“When I joined NASA, we were trying to get into 2012 and we could have at that time,” he said. “But two years have since gone by — it’s no longer the spring of 2005, it’s the spring of 2007 — and so, at this point, the best we could do would be mid 2013.”

To meet that earlier date, Griffin said, NASA would have to spend an additional $2 billion in the years ahead.

Several lawmakers have said they would fight for the extra money for NASA but would prefer the White House make the first move by sending over an amended 2008 budget request. Griffin gave no indication that was about to happen, saying only that the shuttle gap was being discussed with the White House in the context of 2009 budget deliberations.