Computer Sciences Corp., a California-based computer services company specializing in government consulting, will expand into a Landover office park in October, bringing 500 jobs to Prince George's County, company and county officials announced yesterday.

Computer Sciences, which already employs approximately 5,000 people in the Washington area, will service the Federal Emergency Management Agency's National Flood Insurance Program from the Landover facility under a recently awarded five-year, $143 million contract.

Computer Sciences won the contract from Electronic Data Systems of Bethesda in federal competitive bidding, company spokesmen said. The Bethesda company will be phased out of the contract by October, but it is uncertain whether any of the positions for clerks, actuaries, systems analysts, claims examiners and others will be filled by former EDS employes.

Gary Fernandes, a corporate vice president at EDS, said he does not expect any layoffs when his contract runs out. "I suspect that most of the people will be absorbed into other parts of our business," Fernandes said.

"We might very well be receptive to hiring some of them," said CSC spokesman Jim Furlong. "Experienced people would be of use to us."

In a news conference with Prince George's County Executive Parris Glendening, CSC Vice President Karl Hagenau said the new operation will function "like a medium-sized casualty insurance company," with the federal government as the underwriter.

Almost no flood insurance is sold by private insurance companies because of the extreme unpredictability of risk and loss exposure, Hagenau explained. The federal government began the subsidized flood insurance program in 1968.

The operation, which is expected to reach full speed by September, will handle approximately 2 million existing flood insurance policies generating annual premiums of $225 million a year. Locally, CSC is a major supplier of defense and aerospace computer services. Federal contracts account for 57 percent of overall sales.

CSC faces criminal charges in connection with one General Services Administration contract for its Infonet remote computing service. A Justice Department indictment in October 1980 charged the company with false claims and mail fraud in connection with billing calculations on the contract, according to CSC. The trial will begin on May 16 in Federal District Court in Alexandria.

The insurance venture will operate from a 70,000-square-foot space in the Metro Business Center on George Palmer Highway just north of Rte. 50. Hagenau said Prince George's was chosen because of the convenient confluence of Metro, Amtrak and two major highways within a mile of the site. The cost of leasing the building in the partially completed development was also attractive, Hagenau said. The building had been empty since it was erected almost a year ago.