CSX Corp., parent of one of the nation's largest railroad companies, said last week that it plans to eliminate as many as 14,000 jobs over the next four years.

The reduction, which would affect almost one in three employes, is necessary because of competition from other railroads and trucking firms, said Diane Liebman, vice president for communications at CSX Transportation Group.

The railroad, part of giant CSX Corp. of Richmond, Va., operates in 20 states, the District of Columbia and Ontario.

Liebman said the company wants to pare its work force to 30,000 by 1991. The railroad employs between 43,000 and 44,000 workers, she said.

Richard I. Kilroy, the chairman of the Railway Labor Executives Association, said union leaders have discussed the cuts with CSX management.

"We've met with them, and we said we'd meet with them some more," said Kilroy, who alsi is president of the International Brotherhood of Railway, Airline and Steamship Clerks.

"Our productivity is increasing all the time, but at the same time the railroad argues that its profit margin is going down and that's something we have to look at," he said.

The CSX railroad system earned $329 million on revenue of $4.5 billion in 1986. At the end of 1985, the carrier had the most employes and track miles of line of any U.S. railroad, according to the Association of American Railroads.

CSX President John Snow raised the issue of job cuts recently in a company newsletter, Liebman said. "This has not been a secret, believe me," she said. "We are in a very competitive situation."

Noncontract employes would be among the first to lose their jobs.

Liebman said CSX wants to cut 480 jobs this year from the ranks of managerial and staff employes. CSX's noncontract work force numbers about 4,700.

The railroad will make those cuts by asking employes to take early retirement and offer severance packages, she said. "We are not going to fire people," she said.

Kilroy said a reduced work force would present "major problems" for unions. The reduction in employes would diminish union strength and cut into the railroad retirement fund, he said.