PORTLAND, Maine — The Navy is moving forward with construction of a new type of smaller, speedy warship after upending the program by canceling contracts last year, officials said Wednesday.

The Navy's formal requests for proposals issued to General Dynamics Corp.'s Bath Iron Works and Lockheed Martin Corp. on Tuesday call for construction of three Littoral combat ships to be carried out over the next several years.

The Navy envisions a competition in which the winning bidder is awarded contracts for two of the ships while the other gets to build just one ship, Navy Lt. Cmdr. John Schofield said Wednesday.

The Navy, which hopes to build 55 Littoral combat ships, wants the smaller warships capable of operating in shallow, coastal waters to meet threats including modern-day pirates and terrorists. The ships are a key element of the Navy's goal of increasing the size of its fleet to 313 ships.

"The Navy, as it exists today, was designed mostly for fighting in the middle of the big blue ocean. The Littoral combat ship is designed to take the fight right up to the enemy's coastline, and into the country if necessary," said Loren Thompson, a defense analyst at the Lexington Institute.

He described the program as the most significant Navy shipbuilding program over the last decade: "It is the one thing that the Navy is doing that is directly responsive to how the threats have changed."

The shipbuilding program has been plagued by cost overruns, and the Navy's handling of the fast-tracked program has come under criticism.

Two competing versions of the ship are under construction at shipyards in Wisconsin and Alabama. But the Navy put the brakes on the program last year, canceling two additional ships, after costs of the original ships grew from early estimates of about $220 million to more than $300 million apiece.

The Navy now is operating under a congressional cost cap of $460 million per ship, a reflection that the original cost estimates for the ships were too low.

Lockheed Martin's LCS-1 is being built at Wisconsin's Marinette Marine Corp., while LCS-2, overseen by Maine's Bath Iron Works, is being built at the Austal USA shipyard in Mobile, Ala.

Lockheed Martin's version resembles a traditional frigate or destroyer but features a sleek, semi-planing hull, while General Dynamic's version is an all-aluminum three-hulled vessel. But both are powered by steerable waterjets and can reach speeds of about 50 mph.

The Navy envisions them chasing down terrorist speedboats, as well as engaging in mine removal and anti-submarine operations in nearshore waters.

The Navy took the unusual step of ordering one of both types of ships, instead of settling on a single design, and by having them built at smaller shipyards.

So far, production of the first two ships has fallen behind schedule, and it remains to be seen whether either design is capable of achieving the Navy's goals, said Winslow Wheeler, a defense analyst at the Center for Defense Information.

Wheeler questioned why the Navy insists on building more ships before the first two designs are put in the water and run through sea trials.

"The proof will be in the pudding when we see a system that passes operational testing ... for a reasonable price," he said. "That is a long way off."