WASHINGTON — A $242.8 million radar system that Congress refused to approve as a military necessity has resurfaced as the costliest item in the Pentagon’s proposed anti-drug budget for the coming year.

Congressional investigators question whether the shuffle is really a Pentagon salvage operation to save a costly program that otherwise would be scrapped.

“I categorically deny” that allegation, said top Pentagon anti-drug official Michael A. Wermuth.

But Wermuth acknowledged that the Pentagon still sees the southern-looking “backscatter” radar as primarily needed to shield against an attack by enemy bombers flying from Latin America.

Defense officials were unable to persuade Congress to finance the southern portion of the “over-the-horizon” radar system in the 1989 and 1990 fiscal years — when it was touted on military grounds.

Now the Pentagon is promoting the system as a way to locate small planes smuggling drugs over the southwest U.S. border.

The first system — to protect against bombers crossing the Atlantic and drug planes flying up the coast — became operational in Bangor, Maine, on April 24. Facilities are under construction in the western United States and construction is planned for Alaska. Congress has approved those sections, mainly on military grounds.