Though NASA has cleared Columbia for liftoff today - launch attempt No. 6 - after a last-minute inspection of the space shuttle’s engines, the weather was likely to force another delay.

That would mean Columbia had tied its own record for shuttle launch scrubs.

Forecasters expect only a 20 percent chance of good weather for the scheduled 9:46 a.m. (EDT) launch. The main concerns are heavy rain and wind associated with recent storms.

Columbia’s 16-day laboratoryresearch mission has been repeatedly delayed by equipment failures and Hurricane Opal.

The latest setback was a dangerous crack found in a test engine in Mississippi. NASA wanted to make sure Columbia’s engines did not have similar flaws and delayed Saturday’s launch to allow time for ultrasonic tests, which found its three main engines in good shape.

Shuttle test director Bill Dowdell insists age is not a factor in Columbia’s troublesome track record. Columbia made the first shuttle flight in 1981; this will be its 18th trip.

Officials also say Columbia’s recent overhaul is not related to all the mechanical problems of the past 2-1/2 weeks: a leaky engine valve, sluggish hydraulics and a failed computer signal-relay unit - and those are just the problems that caused delays. One of Columbia’s primary computers and a unit that formats computer data also had to be replaced in just the past few days.

xxxx?