WASHINGTON, May 31 — Although there is still a risk of dangerous foam debris, NASA officials cleared the space shuttle's external fuel tank on Wednesday for launching of the Discovery in July, after a year on the ground.

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Scott Audette/Reuters

The Discovery was rolled out to its launching pad on May 19. Its most recent flight, last July, led NASA officials to ground the shuttle fleet.

Shuttle program officials, meeting at the Kennedy Space Center in Florida, said enough modifications had been made on the tank since the last shuttle flight to give them confidence that the foam risk was minor.

N. Wayne Hale Jr., manager of the shuttle program, said at a news conference that foam debris from different areas on the fuel tank would continue to come off and pose some risk of damaging a shuttle. But he called the risk "acceptable" and said, "We have eliminated the largest hazards."

Repeating a note often sounded by NASA officials and astronauts, Mr. Hale said the shuttle would always be risky to fly.

Michael D. Leinbach, the shuttle launching director at Kennedy, said the Discovery should be ready to launch within a window lasting from July 1 through July 19. In the approach to that window, managers will have unusually long contingency time, almost two weeks, to deal with problems that might arise.

Mr. Leinbach also said the shuttle Atlantis was on schedule to roll out to its launching pad on July 25 in anticipation of a mission beginning Aug. 28 or shortly thereafter.

NASA wants to fly the shuttle three times before the end of the year to get back on schedule building the International Space Station before the shuttle fleet's retirement in 2010. After 2006, officials hope to fly four missions a year before the deadline.

A reduction in falling fuel tank debris has been a priority for NASA since the loss of the shuttle Columbia, a disaster that was caused by foam insulation that tore from the tank at launching and punched a hole in a heat shield. Superheated gases entered the hole as the ship re-entered the atmosphere from a science mission on Feb. 1, 2003, destroying the Columbia and killing its crew of seven.

After the accident, NASA spent two years and hundreds of millions of dollars redesigning the tank and modifying methods of applying foam insulation to stop shedding. But when the Discovery flew last July, on the first mission since the Columbia, a greatly reduced but hazardous amount of foam fell from its redesigned tank after launching.

NASA then grounded the fleet, and tank engineers removed more than 37 pounds of foam that had formed two air ramps, or deflectors, that protected pressurized fuel lines and a tray guiding cables down the side of the tank. Those were the areas from which the biggest pieces of foam fell during the last mission.

Mr. Hale said Wednesday that there were other tank parts from which engineers would like to remove foam but that officials had decided it was best to fly with only one major modification at a time, to see if the changes worked as expected.