General Public Utilities Corp. announced tonight that it would stop nearly all of its construction projects to save cash to pay for damages to its Three Mile Island nuclear generating station near Harrisburg, Pa.

General Public Utilities owns several power companies in New Jersey and Pennyslvania, including Metropolitan Edison Co., which operates the Three Mile Island plant.

William G. Kuhns, company chairman, said the steps "are consistent with our accelerated efforts to conserve cash resources as a result of the Three Mile Island Nuclear Unit Number Two accident last Wednesday. We are cutting back on costs and expenses whenever we can possibly do so without adversely affecting our ability to meet immediate customer requirements."

The company carries $300 million in insurance on the nuclear facility, but the total cost of the accident could well exceed that figure. The nuclear plant cost $780 million to build.

In a statement issued tonight from its headquarters in Parsippany, N.J., General Public Utilities said it would suspend immediately construction of a large nuclear station scheduled to go into operation in 1983. It also said it would stop building a coal-fired plant slated to open in 1985.

The $1 billion, 1,100-megawatt nuclear plant is being built in Lacey Township, N.J., by General Public subsidiary Jersey Central Power & Light Co. The 625-megawatt coal-fired plant is in western Pennsylvania.

Besides stopping construction of the two big generating stations, the company also is halting all but the most essential projects at existing plants and postponing all nonessential maintenance programs at its operating power stations.

The $1 billion Forked River nuclear power plant in New Jersey, now about 3 percent complete, is similar but not identical to the Three Mile Island facility.

The Company said it would resume construction of the two plants at some time in the future.

The company said Monday that it expects to borrow heavily during the next few months to cover the "substantial expenditures" expected in the wake of the Harrisburg accident.