Satellite Business Systems, the fledgling, well-financed communications venture, is having a hard time getting itself off the ground.

For the third time in a month, the McLean-based firm yesterday announced a postponement in the launch of the company's first satellite. Essentially, the company's communications operations cannot begin until the satellite lifts off from Cape Canaveral.

A spokesman for SBS, Larry Weekly, said the decisions to delay the launch have been made by officials of the National Aeronautics and Space Administration because of a series of technical problems primarily involving the Delta vehicle.

The satellite, known as SBS 1, and built for exclusive use by the company by Hughes Aircraft Co., is said by SBS officials to be the first of its kind to offer a high-frequency, interference-free signal.

SBS, funded with nearly $400 million by a partnership made up of Communications Satellite Corp., International Business and Aetna Life and Casualty, already has signed up customers such as Westinghouse Corp., The Travelers Corp. and Allstate Insurance Co., which SBS has just announced as a customer for its teleconferencing service.

Although the delays should not affect either the tests of the system, which are to begin by the end of the year, or the start of service, now set for early 1981, Weekly said the three postponements will put "more pressure on the test schedule."

The liftoff of the 2,374-pound satellite was originally was set for Oct. 23, but was postponed after a partial failure of a perigee kick motor, a device that will kick the satellite into a transfer orbit. Insulation on the motor nozzle that peeled away was modified.

The launch then was set for Nov. 6, but was scrubbed after a worker making a routine inspection noticed that a first-state motor was tilted. A fracture was found in a metal bolt attached to a motor on the first stage.

After the launch was rescheduled for Nov. 12 and the company had begun completing elaborate plans to bring to Florida many SBS customers and potential subscribers, a leak of liquid oxygen was discovered, once again delaying the operation. SBS now expects to get its satellite, and presumably its operations, off the ground by Nov. 19.