The Reagan administration and environmentalists disagreed yesterday over whether a new wildlife refuge should be established at the southern tip of Virginia's Eastern Shore.

Rep. Herbert H. Bateman (R-Va.) and The Nature Conservancy, an Arlington-based conservation group, called for immediate action that would establish a 1,400-acre refuge at Cape Charles, one of the major locations for concentration for migratory birds along the East Coast.

The refuge site is threatened with development unless the federal government steps in, Nat Williams of The Nature Conservancy told a congressional hearing. "It is unmistakably the key area in the preservation of migratory hawks, shore birds and songbirds, not just on the Eastern Shore, but quite possibly for the whole Eastern United States," he said.

The Reagan administration opposed acquiring the land because of its cost, estimated by Bateman at $3.6 million. F. Eugene Hester, deputy director of the Fish and Wildlife Service, said the agency would like to establish a wildlife refuge there someday.

"That is a high priority on the Eastern Shore," he said. "We do consider it a priority but not one of our highest priorities" nationwide.

An Interior appropriations bill approved this week by the House Appropriations Committee included $2.6 million for the refuge if Congress authorizes the project, according to Williams. A staff member for the House subcommittee on fisheries and wildlife conservation, which held yesterday's hearing, said that the money bill could be voted on later this month.

The Fish and Wildlife Service already owns the abandoned 174-acre Cape Charles Air Force Station, part of the proposed refuge site. The bill would allow the service to buy adjacent land owned by the Chesapeake Bay Bridge and Tunnel District and the Wise Point Corp.

The bridge-tunnel authority has placed its adjoining 400 acres on the market, and an offer has been made by a development company. This alarmed Northampton County officials, who asked Bateman and The Nature Conservancy for assistance.

As birds migrate south along the Atlantic Coast, they tend to concentrate at two points, Cape May in New Jersey and Cape Charles. A series of smaller preserves already has been established at Cape May.

Many birds rest and feed at Cape Charles while they wait for favorable wind patterns before making the 17-mile crossing of the Chesapeake Bay.