Communications Satellite Corp. has announced plans to build a $50 million earth station complex in central Pennsylvania in conjunction with four other major telecommunications companies.

Half ownership of the facility, which will be one of most expensive earth station sites ever constructed, will be held by Comstat and the rest by the other members of a consortium, which includes American Telephone & Telegraph Co., International Telephone & Telegraph Co.'s Worldcom subsidiary, RCA Globcom and Western Union International, Comsat said.

The earth station complex, located 10 miles south of Bloomsburg, Pa., is designed to handle the continuing growth in satellite communication signals, particularly between the United States and other nations in the Atlantic region.

Traffic between the U.S. and the Atlantic Ocean region makes up almost 85 percent of all U.S. satellite traffic, and these signals, consisting of telephone calls, television, facsimile and data services, are expected to double by 1985, Comsat said.

"This facility is key to Comsat's continuing ability to meet the growing need in the United States for reliable international satellite communications," said Robert Kinzie, a vice president of Comsat World Systems.

Despite the growth in traffic, there are only two earth station sites on the east coast to handle the signals. the new facility, with three satellite dishes, will handle the traffic growth and will be available as a backup for the other two sites, located at Andover, Mass., and Etam, West Virginia.

The new station will be able to communicate with any of three satellites positioned over the Atlantic Ocean, but generally will only operate with one of them, Intelsat V, a fifth generation satellite of the International Telecommunications Satellite Organization, a group of 106 countries who share communications facilities.

Comsat is a District-based satellite concern that is expanding its operations into business communications through a partnership, Satellite Business Systems, and into television programming through Satellite Television Corp.

The company's current plans for the Pennsylvania station include the construction of three antennas 105 feet in diameter and a 30,000-square-foot control center for the electronic equipment necessary to run the operation.

Comsat and the other members of the U.S. Earth Station Ownership Consortium, have secured an option for the site. The companies must still receive approval from a local zoning board in Cleveland Township, Pa., and from the Federal Communications Commission. Comsat said the facility would employ about 30 people and have an annual payroll of more than $500,000 when operations are expected to begin in 1983.