Washington - Nasa remains committed to its part in assembling the International Space Station (ISS), but will use the least number of space shuttle flights in a bid to limit costs, the American space agency's head said on Monday.

Nasa also will cut back on ISS research to shift funds to the shuttle's planned successor, Nasa Administrator Michael Griffin told reporters, citing US Congressional pressure to get it flying "as soon as possible after 2010", when the space shuttle is to be retired.

Nasa is moving up its target year for the shuttle successor, the Crew Exploration Vehicle (CEV), from 2014 to no later than 2012. Plans also include repairing the ageing Hubble space telescope, Griffin said.

"Nasa has asked industry for proposals to bring the CEV online as close to 2010 as possible and not later than 2012," he said.

The space agency's proposed budget for the fiscal year starting October 1, unveiled on Monday, calls for a 3,2-percent spending increase.

The research budget is to rise only by one percent, but Griffin rejected suggestions that Nasa is shifting away from research to focus on President George Bush's ambitious goals for human space exploration. - Sapa-dpa