(Adds quotes from prepared testimony, details, background)...

(Adds quotes from prepared testimony, details, background)

WASHINGTON, May 3 (Reuters) - The U.S. Navy has decided to delay by a year until fiscal 2020 the awarding of a design and construction contract for a planned new frigate, according to congressional testimony on Wednesday by two Navy rear admirals.

The delay resulted from a decision to set up a frigate evaluation team to look at how to make the vessel more lethal and survivable, Rear Admirals Ron Boxall and John Neagley said in their prepared testimony.

Navy analyses have determined that the U.S. fleet needs 53 small surface combat ships to supplement the larger aircraft carriers and destroyers, undertaking tasks like antisubmarine warfare and mine countermeasures.

The Navy initially approved two different designs for so-called Littoral Combat Ships, or LCS - one a monohull developed by Lockheed Martin LMT.N , and the other a trimaran hull developed by General Dynamics GD.N and built at an Austal USA (ASB) shipyard in Alabama.

Both were designed to be modular, so they could be quickly refitted to take on different roles.

Both variants of the LCS faced initial production and operational difficulties and have been criticized by the Government Accountability Office for not being lethal or survivable enough in combat.

The vessels displace about 3,000 tons and are about the size of a light frigate or Coast Guard cutter, according to the Congressional Research Service. They cost about $480 million per ship.

The Pentagon restructured the program in response to criticism in 2014, deciding to go ahead with the construction of 32 LCS. The remaining small surface combat ships would be built with a revised design to improve their combat ability.

The new ships would be called frigates and the older LCS would be relabeled frigates once they were retrofitted with the capabilities of the newer ships. The new vessels were supposed to start being built no later than the 2019 fiscal year.

Boxall, the director of the Navy's surface warfare division, and Neagley, head of the LCS program office, told a subcommittee of the House Armed Services Committee that the Navy had decided to establish a frigate evaluation team to look at upgrading the warfighting capabilities of the current frigate design.

"The Navy is defining the requirements for the frigate to improve its ability to operate in a more contested environment than LCS," they said in their statement.

They said the Navy planned to award a contract for the ships by the 2020 fiscal year.