NASA delayed shuttle Endeavour's liftoff for the international space station Thursday to make sure there's no danger from an improperly docked Russian supply ship.

The launch delay was announced nine hours before scheduled liftoff. A security ban on small planes in the area was continued through Friday night.

Shuttle managers decided to give engineers until Friday to make sure no damage would result from Endeavour's own docking with the station. Because of the forces involved in a shuttle docking, engineers were concerned that a wobbly supply ship might harm the station.

NASA also had to worry about the repairs that will be necessary, by a pair of spacewalkers, to remove a stray cable and secure the supply ship to the station. Managers may opt to delay Endeavour's launch until after the spacewalk, possibly early next week, said Jim Van Laak, a space station manager.

Endeavour had been scheduled to blast off Thursday evening on a mission to exchange crews aboard the space station. The problem with the newly arrived supply ship arose late Wednesday, shortly after the vessel linked up with the 250-mile-high outpost.

Fighter jets, attack helicopters and military personnel in camouflage provided an unprecedented backdrop for the launch. Air Force officials promised the same level of security for Friday evening's launch attempt to protect against possible terrorist attacks.

Russia's Mission Control outside Moscow suspects a cable may be blocking the docking mechanism between the space station and its Progress supply ship. Space officials there are proposing that two station crew members go out on a spacewalk to try to clear the area, possibly early next week, said NASA spokesman Kelly Humphries.

A spacewalk could be conducted while Endeavour is docked to the station, Humphries said.

"The Russians have told us they believe it's safe for us to dock," Humphries said. "But we are continuing our analysis ... to make sure that we agree."

Space station commander Frank Culbertson and his two Russian crewmates told flight controllers they could see a cable floating from where the supply ship was attached. "Good luck to you guys," a Russian flight controller radioed.

Endeavour is to drop off three men for a half-year stay and bring back Culbertson and his crewmates, who have been on the station since August. The shuttle also will carry thousands of U.S. flags in tribute to those killed in the Sept. 11 terrorist attacks.

Good weather was forecast for Friday's launch attempt, and the shuttle was looking in top form. NASA halted the countdown just before the launch team was to begin loading fuel into Endeavour's giant tank. The seven astronauts had yet to board.

Air Force officials say they're doing everything reasonable to protect Endeavour from a terrorist attack, especially once its external fuel tank is loaded with more than 500,000 gallons of liquid hydrogen and liquid oxygen and its crew climbs aboard.

In addition to the military show of force, the Federal Aviation Administration prohibited small planes from flying within 35 miles of the launch pad, extending the ban through Friday night and, in effect, shutting down local airports. The previous limit was six miles. All boaters were ordered to stay at least three miles offshore Friday night.

"This is an unprecedented level of effort and certainly is appropriate considering that the United States is at war and this is an area where we know terrorists did frequent," said Air Force Col. Sam Dick, vice commander of the nearby 45th Space Wing.

Many of the terrorists who hijacked the jetliners lived and operated in Florida -- "and there could be others," Dick warned this week. He refused to say whether any threats have been made against Kennedy Space Center or the space shuttle.