CAPE CANAVERAL, Fla. -- The chances of NASA launching the space shuttle Atlantis this week diminished by the hour Sunday as the space agency worried about the effect of a lightning strike at the launch pad and the threat of Hurricane Ernesto.

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NASA delayed the launch until Tuesday to give engineers more time to figure out if the lightning strike Friday damaged the spacecraft's solid fuel rocket boosters and other systems.

However, the threat of Hurricane Ernesto was diminishing the chances of a shuttle launch for later in the week.

The lightning didn't hit the shuttle, but it struck a wire attached to a tower used to protect the spacecraft from such strikes at the launch pad. Engineers wanted time to check out some readings on ground and flight systems.

"The lightning actually hit the top of the launch pad structure," Local 6's Erik von Ancken reported. "The shuttle is attached to the structure (hit by lightning) and that is why engineers are checking, testing and evaluating all of the electronics."

The lightning strike was one of the most powerful ever to hit a launch pad at the Kennedy Space Center, said Leroy Cain, launch integration manager.

"(The strike) could cause us to retest some of the systems onboard the ship if we decide to do that," launch Director Mike Leinbach said.

"We know just enough to know that we don't know enough to press on into a launch situation," Cain said.

NASA managers also had been concerned about storms passing through the area before launch time Sunday.

Shuttle weather officers had said earlier in the day that there was a 60 percent chance the weather would prevent the shuttle from blasting off at the scheduled launch time of 4:30 p.m. EDT Sunday. NASA won't launch if there are storms within 23 miles of the shuttle landing runway, in case astronauts need to make an emergency landing.

The forecast was expected to improve dramatically for Monday and Tuesday, with only a 20 percent chance that weather would prevent a launch on either of those days. NASA plans had four potential launch times over five days.

Shuttle weather officers also were tracking Tropical Storm Ernesto, which was likely to enter the Gulf of Mexico on Tuesday or Wednesday and threatened to reach hurricane strength. Ernesto wasn't expected to affect a launch early in the week, but it could cause problems if Atlantis doesn't lift off until later in the week.

In a worst-case scenario, if Ernesto were to strike Texas after the shuttle's launch and workers were forced to evacuate Mission Control in Houston, the shuttle astronauts would have to leave the station and return to Earth at the first opportunity. An evacuation would mean flight controllers couldn't sufficiently support a mission as complex as this, which will attach an addition to the space station, NASA managers said.

In that situation, NASA controllers and the astronauts would make every effort to leave the 171/2-ton addition the shuttle is carrying at the space station. That $372 million addition has two solar power wings that eventually will provide a quarter of the station's electricity.

"If we had to evacuate (Houston) ... we would not be able to execute the docked mission. ... Certainly not of the complexity of the one we're about to embark on," said Cain. "We would leave the station in the safest configuration and come back and pick up the pieces ... on a subsequent mission."

Construction of the half-built space station has been on hiatus since the 2003 Columbia disaster, which killed seven astronauts. Atlantis' mission is the first of 15 flights scheduled to finish building the space station before the cargo-carrying shuttles are retired in 2010.

"We have to let this one occur before the next ones can go," said Mike Suffredini, NASA space station program manager. "This is clearly in the critical path for success in assembly."

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