An independent panel overseeing NASA's resumption of shuttle flights concluded yesterday that the space agency has failed to meet the toughest safety recommendations put in place after the 2003 Columbia disaster.

Despite exhaustive work and considerable progress over the past 2 ½ years, NASA has been unable to eliminate the possibility of dangerous pieces of foam and ice from breaking off the external fuel tank and striking the shuttle at liftoff, the return-to-flight task force said.

In addition, NASA still does not have a clear idea of all the potential threats from ice, and still lacks a practical way to fix holes and other damage caused by flyaway launch debris, the group said.

However, it said the orbiter is nevertheless "ready to fly" and praised NASA for its exhaustive efforts to overcome the critical flaws that caused the Columbia tragedy.

NASA has been aiming for a liftoff of Discovery as early as July 13 on the first mission since Columbia's destruction during re-entry on Feb. 1, 2003.

The group's chairman, Richard Covey, a former astronaut, stressed that the three recommendations debated yesterday represented the most technically challenging of the 15 put forth by Columbia accident investigators as being essential for the resumption of shuttle flights.

"You have to look at the progress that has been made," Covey said at a news conference. "Is it a miss if you're at 95 percent? We haven't seen anything that says that [there is] any danger to the vehicle."

It was not immediately clear if NASA would proceed with its planned July shuttle launch.