WASHINGTON -- With soaring rhetoric and surrounded by astronauts, President Bush yesterday pushed for a vast new commitment to space exploration, including putting settlements on the moon and making a manned flight to Mars.

But he provided no estimate of the total cost of the commitment or how it would be paid for.

"We do not know where this journey will end, yet we know this: Human beings are headed into the cosmos," he said to loud applause at NASA headquarters. The speech was clearly designed to lift the nation's spirits in an election year. Bush and White House aides used the word "vision" repeatedly yesterday in talking about it.

Bush presented a bold and ambitious schedule.

NASA would develop and build a new "crew exploration vehicle" to ferry people first to the space station after the shuttle fleet is retired by the end of the decade, and then to the moon.

By 2008 robotic missions will go to the moon, followed by manned flights in 2015 with the moon becoming a place where astronauts will live and a launchpad for expeditions beyond Earth's orbit. Bush did not set a timetable for going to Mars.

Although the cost of going to Mars 14 years ago during President George H.W. Bush's administration was estimated at $500 billion and deemed too expensive, the current president said restarting the program, as his father wanted, was feasible by increasing NASA's budget 5 percent a year.

Bush said it could be done by carving out $11 billion of NASA's $86 billion five-year budget and spending an additional $1 billion over five years. The Center for American Progress said that in today's dollars, the president's space initiative would cost at least $700 billion.

A recent Gallup poll found that Americans love the idea of going to Mars, but that two-thirds are unwilling to spend a lot of money for it.

Bush invoked the adventurous spirit of the Lewis and Clark expedition to the American West 200 years ago and said space travel was the modern equivalent. He noted that the rover Spirit is now on Mars "searching for evidence of life beyond the Earth."

Some scientists have said there is no need for humans to risk going back into space because robots can do the same tasks; Bush disagreed. "The human thirst for knowledge ultimately cannot be satisfied by even the most vivid pictures or the most detailed measurements. We need to see and examine and touch for ourselves. And only human beings are capable of adapting to the inevitable uncertainties posed by space travel," he said.

The initiative comes after a bad year for manned space exploration that included the breakup of the space shuttle Columbia killing all seven astronauts on board and a devastating report by the Columbia Accident Investigation Board that blamed NASA management for cutting corners on safety.

In embarking on the plan, Bush clearly intended to boost morale at NASA as well as strike a political coup by appearing visionary and above politics at the same time Democrats are embroiled in the fiery politics of the Iowa caucuses.

After the White House told reporters last week that Bush was ready to outline his long-awaited space vision, a huge debate erupted in Congress and in academia on the merits -- whether it is too dangerous (24 astronauts have died), whether the scientific knowledge justifies loss of life, and whether the nation can afford hundreds of billions of dollars on space exploration when it has a deficit.

But yesterday at NASA headquarters, a clearly invigorated Bush insisted the nation must commit to a new course of space travel, moving from robotic missions to manned ones in an adventure that he vowed would pay huge benefits.

Bush said there is evidence of water on Mars and there could be materials on the moon that could be used for rocket fuel and even breathable air. He said a station on the moon would save money by reducing the fuel costs of pushing a space vehicle out of Earth's gravity.

The president was welcomed to NASA headquarters by astronaut Michael Foale, who addressed him by videophone from the International Space Station, 240 miles above Earth.

Bush emphasized that revitalizing the space program would provide technological breakthroughs not yet imagined. He noted that so far space exploration has yielded advances in weather forecasting, communications, computing, search and rescue techniques, the global positioning system and robotics.

Bush saluted former astronaut Eugene Cernan, the last man to set foot on the moon who sat, white-haired and solemn in the audience. Cernan said as he left the moon in 1972, "We leave as we came and, God willing, as we shall return: with peace and hope for all mankind."

Bush vowed, "America will make those words come true."