The first commercial launch of a Martin Marietta Titan rocket in 1989 will carry a British communications satellite, the Bethesda-based aerospace giant announced last week.

The agreement to carry the British Skynet 4 satellite into space represents the fourth such commitment for Marietta and another step in the U.S. effort to shift the launching of satellites from the National Aeronautics and Space Administration to private companies.

The price the British Ministry of Defense wil pay for the launch of the 3,230-pound satellite has not yet been negotiated, a Marietta spokesman said.

However, the cost of a typical Titan launch is about $110 million, he said. The commercial Titan, a derivative of the Titan III rocket that long has carried U.S. military payloads, is capable of carrying two satellites at a time and can deliver more than 31,000 pounds into orbit, Marietta said.

The first commercial Titan flight, scheduled for liftoff from Cape Canaveral, Fla., in August, 1989, also will carry a Japanese communications satellite, as previously announced. Marietta also has contracts to launch two satellites for the International Telecommunications Satellite Organization (Intelsat) in future trips.

The agreement with the British is the second piece of good news for Marietta's commercial space efforts in the past two weeks. On Oct. 26, the Air Force successfully launched a Marietta-built Titan 34D, ending an 18-month grounding of the rocket. Marietta said the Titan has recorded 131 successes out of 136 operational launches for the Air Force.

In the past, satellites like the British satellite have been launched aboard NASA's space shuttle or the European Space Agency's Arian rocket. However, after the Challenger disaster in 1986, President Reagan announced a policy that restricted the shuttle to carrying military and scientific payloads.

As a result, Marietta and several other U.S. firms, including General Dynamics Corp. and McDonnell Douglas Corp., have started to compete for the international rocket launching business previously done by NASA.

Marietta said the British Defense Ministry was the first in Europe to select the Titan to put a military communications satellite in space. Marietta's spokesman said the company also is negotiating with several other European satellite makers.