President Bush's call for moon missions and journeys to worlds beyond is what NASA and space enthusiasts have been hungering to hear. But even supporters wonder how the agency will cover a tab that's sure to soar into the hundreds of billions of dollars.

"I hope that by the president making this announcement, he'll put the horsepower behind it and sustain it for the long run," said Sen. Bill Nelson (search), D-Fla., the only current member of Congress to fly in space.

But from what Nelson heard Wednesday, the horsepower isn't there.

Bush is proposing an extra $1 billion for the National Aeronautics and Space Administration (search) over the next five years for the new space initiative, an amount Nelson says is "nowhere close" to what will be needed.

The president also has directed NASA to reallocate $11 billion within its budgets over the next five years to cover the startup costs of sending astronauts back to the moon and, eventually, on to Mars.

The goal is to land astronauts on the moon as early as 2015 and no later than 2020. Neither Bush nor NASA Administrator Sean O'Keefe offered a timetable Wednesday for putting humans on Mars, and neither offered specifics on the spacecraft that would replace the shuttle and carry astronauts beyond low-Earth orbit.

"Today we set a new course for America's space program," Bush said in a speech at NASA headquarters that was interrupted several times by applause. "We will give NASA a new focus and vision for future exploration. We will build new ships to carry man forward into the universe, to gain a new foothold on the moon and to prepare for new journeys to the worlds beyond our own."

Bush's election-year initiative represents the boldest space goals since President Kennedy laid the groundwork for the Apollo program (search) that landed Americans on the moon in 1969, just eight years after the president committed the nation to the daunting goal.

At a meeting Thursday with NASA employees, O'Keefe said the space exploration decisions were reached after months of intensive discussion among government officials from the White House, NASA and other agencies.

Bush, said O'Keefe, was "inquisitive" throughout the decision process and was aware of all of the options. The president's decisions, said O'Keefe, came after "lots of intensive thinking" by Bush.

Intended to inject new life into a space program shattered by last February's loss of the space shuttle Columbia and its crew of seven, Bush's proposal will require major technological advances, and it faces tough questions in Congress. Many Democrats say the administration should take care of problems at home before setting its sights on costly space initiatives, particularly in the face of budget deficits of about $500 billion.

House Minority Leader Nancy Pelosi, D-Calif., said the new space plan will face tough scrutiny. "As we go forward with any initiative we have to examine our priorities," she said. "We have serious challenges here on Earth."

And while professing support for space exploration, Sen. Edward Kennedy, D-Mass., said, "We shouldn't be going to outer space and sacrificing what we need to do here."

An AP-Ipsos poll this week found the public evenly split on Bush's plan. Just over half of Americans said it would be better to spend the money on programs like education and health care rather than on space research.

Bush's father, the first President Bush, used the 20th anniversary of the first manned moon landing to call for moon colonies and a Mars expedition, but that less-detailed plan went nowhere. The estimated cost: $400 billion to $500 billion.

John Glenn (search) figures the price in today's dollars might be close to double that, "at a time when we are running unprecedented deficits." The retired Democratic senator, the first American to orbit the Earth, would much rather see the International Space Station (searchcompleted and operating at full capacity, as promised by the Clinton administration.

Under Bush's plan, the space shuttles would be phased out in 2010, the same time that the space station is finally finished with a minimum of U.S. input. A new spacecraft called the crew exploration vehicle would take over by 2014, capable of carrying astronauts not only to the space station but "beyond our orbit to other worlds," the president said.

To carry out his program, Bush formed a new panel, the Commission on the Implementation of U.S. Space Exploration Policy (search), to advise NASA. Pete Aldridge, a former Air Force secretary, was named to lead the effort.

The lunar push will begin no later than 2008 with a series of trailblazing robots, the president said. He stressed that humans will follow.

Some scientists contend it would be more efficient and less expensive to use robots instead of astronauts for exploring the solar system, like the Spirit rover (search) on Mars right now.

John Young, among nearly 20 astronauts who attended Bush's speech, said the initiative is slower and more deliberate than the Apollo program that put him on the moon in 1972. "But developing the technologies is crucial. I think we can do that very cheaply and very fast," he said.

A methodical approach is exactly what's needed this time around, said Apollo 17 astronaut Gene Cernan, the last man to walk on the moon, in December 1972.

"He said he once again wants to make NASA relevant. That says a lot," Cernan said.