The General Accounting Office, in a report expected to fuel congressional controversy, has issued a detailed challenge to the Navy's strategic rationale and cost projections for the new ports the Navy plans to open in eight states.

The GAO found that the Navy's plans to cluster two carrier groups and three battleship groups in new ports could expose them to greater danger at some locations without significantly improving fleet readiness, training or logistics.

The report, which has not been published, said the Navy will have to spend hundreds of millions of dollars more to construct the new ports than the $799 million it has projected. Considerable savings could be realized, the GAO said, by using existing facilities that have room to grow and already are scheduled for expansion.

Concluding that the Navy has not "adequately demonstrated" the strategic benefits of the new ports, the report urged Congress to demand more detailed analysis before approving funds.

Navy Secretary John F. Lehman Jr. said in an interview that the chief benefit of opening new ports is "self-evident: dispersed targets are less vulnerable." He chided the GAO for exceeding its charter by engaging in naval strategic analysis.

Lehman said that while construction of new ports will be 20 percent costlier than the use of existing facilities, the costs can be justified in enhancing fleet security.

Lehman began opening new ports in 1982 to service refurbished battleships. Bypassing Sun Belt and West Coast ports where the fleet has been concentrated for decades, he chose new facilities at Staten Island, N.Y.; Everett, Wash.; northern California, and the Gulf Coast.

Besides complicating enemy targeting, Lehman has said, fleet dispersal will place ships closer to potential conflict zones and diversify training environments.

Congressional opponents contend that Lehman's port expansion plan is intended to bolster support in Congress for the 600-ship fleet he wants built by 1990. Opponents of Lehman's efforts to disperse the fleet include those from traditional Navy ports, such as Sen. Strom Thurmond (R-S.C.), who requested the GAO study.

Instead of enhancing security, the GAO said, fleet dispersal could increase the risk of mining and sabotage because most new facilities are planned for ports open to Soviet commercial ships. Many of the Navy's existing ports exclude Soviet vessels, it said.

Lehman said in the interview, however, that all Navy ports are open to Soviet merchant vessels.

Some new ports would place ships closer to potential regions of conflict, the report said, but Gulf Coast vessels would not get to Central America any faster than warships now berthed along the southeast coast. They also would need more time to reach the North Atlantic, the GAO said.

The report said that the new ports are not expected to significantly diversify training environments because the Navy has not indicated plans for new test ranges outside the traditional Caribbean and southern California areas.

The Navy's estimates of$799 million for construction of the new ports is "understated," the report said, because they include only the costs of basic port construction. The projections do not cover the costs of outfitting and operating the new facilities, it said.

Architectural and engineering studies prepared for the Navy, the GAO said, show that the construction costs of the Staten Island and Everett facilities alone could reach $838 million.