Last-minute complications with a weak battery and a faulty guidance system tonight forced a 24-hour delay in the scheduled test launch of America's first commercial space venture.

The decision to set back Wednesday's sub-orbital flight was made less than 12 hours before its scheduled firing time by retired astronaut Donald K. (Deke) Slayton, vice chairman of Space Services Inc. of America, a Houston-based firm that is behind the project.

"We could have pressed and tried to hold it tomorrow, but the guys were too damn tired," Slayton said here late tonight. "We're going to back off a day, get things stuck in and checked off."

The unexpected setback came as the launch crew of the 37-foot, solid-fuel rocket, dubbed Conestoga I, carried out its final tests and preliminary countdown. It was during that countdown that the crew discovered the weakness in the battery and what Slayton described as a "sticky platform" on the roll axis that helps guide the rocket once launched.

SSI officials made arrangements to have a battery flown in from California, but later Slayton decided to scrub Wednesday's launch in favor of one at 11 a.m. EDT Thursday.

Earlier in the day, all appeared ready for the first successful flight of the good ship free enterprise, and SSI officials spent much of today showing off their rocket and surrounding electronic gear to a horde of reporters, photographers and television technicians.

At that time, there was no talk of problems, other than the weather and, perhaps, an errant aircraft flying over the test site at launch time. "The hardware we don't expect to have trouble with," Slayton said at a pre-launch news conference held under a tent in the middle of a field on Matagorda Island about 45 miles northeast of Corpus Christi.

"If there's trouble," he said then in his typical self-confident style, "we'll fix it."

A year ago, SSI's first test flight ended in failure when a liquid-fuel rocket built by a California firm blew up on the launch pad. This year, with a solid-fuel booster purchased off the shelf from the National Aeronautics and Space Administration and a more professional crew headed by Slayton and a host of expert subcontractors, the chances of success have appeared better, despite tonight's delay.

The 10-minute flight, which will carry the rocket 189 nautical miles up into space and 289 miles out into the Gulf of Mexico, has drawn worldwide attention, as SSI seeks to become the first private U.S. firm to offer inexpensive transportation into space for corporations that want to put up their own satellites.

"I'm amazed. I'm astounded," said David Hannah, chairman of SSI, referring to the interest in his project. But he acknowledged that the attention carried one significant disadvantage.

"It's always easier to fail when no one's watching," he said.

The scene on the island today showed how far Hannah's company has progressed in one year. Gone from last year's test are the garden hoses and the milk crates and, apparently, an alligator named Ralph who watched from a pond near the original launch pad.

In their place are several other private companies with experience in launching and tracking space vehicles, and an array of electronic equipment housed in trailers and containerized crates that were shipped to the United States from West Germany.