NASA unveiled a 13-year, $104 billion blueprint today for sending humans back to the moon as early as 2018, using modified space shuttle rockets to loft an Apollo-like capsule into space.

Space analysts said the design was decidedly retro, hearkening back more than three decades to the Cold War's moon race.

But they said the new design was safer and more realistic than the current space shuttle, which is scheduled to be retired in 2010 after nearly 25 years of service and two disastrous shuttle losses.

"Think Apollo on steroids," National Aeronautics and Space Administration head Michael Griffin said during a news conference at the agency headquarters in Washington, D.C.

The new capsule, known as the Crew Exploration Vehicle, will be significantly larger than the cramped Apollo capsule, with seating for as many as six astronauts instead of three.

The new vehicle, slated for its maiden launch in 2012, initially would be used to resupply and transfer crews from the International Space Station after the shuttle is retired, NASA officials said.

Unlike the winged shuttle that was mounted on the side of the rocket, the capsule would sit atop the rocket, away from falling debris and potential engine fires that destroyed the shuttles Columbia in 2003 and Challenger in 1986.

NASA officials estimated the new craft would be 10 times safer than the space shuttle. The agency estimates that a space shuttle will be lost about every 220 missions. The new vehicle will be designed to go more than 2,000 missions without a serious calamity.

In 2018, NASA would launch the first back-to-the-moon mission with new lunar landers and other components that would allow for as many as four astronauts to stay on the surface for as long as seven days.

The Apollo missions, which cost $150 billion, focused primarily on landing astronauts on the moon for a day or two and then returning them safely to Earth.

The blueprint unveiled today is part of a broader initiative launched by President Bush 18 months ago, in which he called for returning humans to the moon as a stepping stone to a manned mission to Mars, perhaps as early as 2020.

Elliot G. Pulham, president of the nonprofit Space Foundation, a space exploration advocacy group, called the blueprint a "challenging yet realistic plan" that doesn't "break the bank."

But questions about how NASA would be able to sustain public interest and win funding from Congress for more than a decade dogged the unveiling today.

Some observers worried that huge federal spending in the future on priorities such as rebuilding New Orleans, which could cost as much as $200 billion, could undermine funding for any major space initiatives.

"If you're not going to have a lunar landing until 2018, how are you going to keep people and Congress interested?" said John Pike, a space policy analyst for GlobalSecurity.org.

But Griffin said the nation could afford the cost despite the hurricane-related expenses because he would not seek any new money for the agency's annual $16-billion budget.

Instead, spending within NASA's human spaceflight program would be redirected to pay for the endeavor, he said. About $4 billion to $5 billion a year is now allocated for manned spaceflight.

Measured in constant dollars, the $104-billion price, spread over 13 years, represents 55 percent of what the eight-year Apollo program cost, Griffin said. The objective, he said, was to "pay as you go and what you can afford."

"There will be a lot more hurricanes and a lot more other natural disasters to befall the United States," Griffin said. "We must deal with our short-term problems while not sacrificing our long-term investments in our future."

NASA's announcement created a buzz among enthusiasts attending the International Lunar Conference in Toronto.

"We've got to go (back to the moon)," said Buzz Aldrin, a former Apollo astronaut who traveled to the moon with Neil Armstrong. "But we don't want to stay too long. ... The ultimate goal is Mars."

On its return to Earth, the spacecraft would be able to touch down on land instead of splashing down in the sea. It would be capable of being reused several times.

"Much of it looks the same," Griffin said, but he added, "It's a significant advancement over Apollo."

The return mission to the Moon will also differ from Apollo in several ways.

Unlike the Apollo program, which relied on massive Saturn V rockets to loft both the capsule and the lunar lander, NASA plans to send up two rockets, one carrying the crew capsule and the other the lunar lander.

The rocket to lift the crew capsule into space would be a modified solid rocket booster used on the space shuttle, while the lunar lander would be carried into space by a rocket made from a modified shuttle engine and external fuel tank.

Once in orbit, the two spacecraft would rendezvous before making the journey to the moon. The new lunar lander, which would be developed later, would be able to carry four astronauts to the moon's surface, compared with two on Apollo.

NASA officials said using Apollo concepts and shuttle technology with the latest advances in materials, propulsion and avionics would allow the agency to meet the president's goals more efficiently and less expensively.

NASA said about 85 percent of the shuttle workforce probably would be retained for work on the new craft.

"We believe this venture safer and more affordable than any other spaceflight ventures that the U.S. has had," Griffin said.