CAPE CANAVERAL, NOV. 15 -- The space shuttle Atlantis, carrying five military astronauts and a Pentagon spy satellite, rocketed into orbit under a veil of secrecy tonight to kick off NASA's last fully classified shuttle mission.

Carrying what some analysts say is a military satellite bound for duty over the Persian Gulf, Atlantis lifted off at 6:48 p.m. EST and headed due east over the Atlantic Ocean.

Although two more military shuttle flights are planned next year, the payloads of both have been declassified, allowing NASA and the Air Force to do away with costly security operations that an Air Force source said total about $80 million a year.

The launch originally was planned for July, but Atlantis was grounded by an elusive hydrogen fuel leak. Several such leaks sidelined its sister ship Columbia in May and September, but both shuttles were repaired and recently cleared for flight. Columbia is being readied for a fifth attempt to launch its long-delayed astronomy mission, probably in early December.

Atlantis's liftoff on the 37th shuttle mission came just three days after Monday night's launch of an unmanned $173 million Air Force Titan 4 rocket from the nearby Cape Canaveral Air Force Station, successfully boosting what was widely reported to be a $180 million missile early warning satellite into orbit.

"What a tremendous week for the Air Force -- two marvelously successful launches," said Lt. Col. Jim Jannette, an Air Force spokesman.

Strapped in aboard Atlantis were commander Richard Covey, a 44-year-old Air Force colonel, co-pilot Frank Culbertson, 41, a Navy commander, Air Force Lt. Col. Carl Meade, 39, Marine Col. Robert Springer, 48, and Army Maj. Charles Gemar, 35.

Under the Pentagon-imposed news blackout, NASA did not reveal Atlantis's exact launch time until nine minutes before liftoff, and all radio traffic between the astronauts and mission control in Houston was blacked out.

But as usual with such military flights, reporters and area residents were able to follow the progress of the countdown by monitoring government UHF radio traffic at the spaceport, including an emergency backup transmitter aboard the shuttle itself.

"Thanks a lot, Bob. We're ready to get out of town," Covey radioed to launch director Bob Sieck shortly before liftoff.

The mission duration is classified, but reliable sources said that if all goes well, Atlantis will glide to a touchdown at Edwards Air Force Base, Calif., at 3:43 p.m. PST Monday.

The goal of the flight also is classified, and there is some difference of opinion among experts about exactly what it is. According to published reports and some analysts, on the second or third day of the mission, Covey and company plan to launch a military satellite that may be used to spy on Iraq.

Aviation Week & Space Technology magazine reported last month that the payload was equipped with a variety of sensors, including digital cameras that might be used to monitor activities in the Persian Gulf region.

But an Air Force spokesman said the shuttle was launched into an orbit that will carry it no more than 28.5 degrees to either side of the equator, well south of Iraq much of the time.

For that reason, John Pike of the Federation of American Scientists in Washington speculated before launch that Atlantis's hush-hush cargo might be an electronic eavesdropping satellite, called Magnum, rather than a photo-reconnaissance craft.