WASHINGTON – Growing ballistic missile threats from rogue states and concerns about ballooning costs were behind the Navy’s recent decision to end a new destroyer fleet after just two ships, a senior service official said last week.

While the Zumwalt destroyer meets the requirements it was designed for, such as providing heavy cover fire to help Marines move ashore, the Navy found increased “gaps” in its warfare capabilities, said Vice Adm. Barry McCullough, deputy chief of naval operations.

Specifically, the Zumwalt cannot perform ballistic missile defense or deploy standard missiles, which the Navy will need to effectively battle potential adversaries that are developing stealth submarines and related offensive threats, McCullough told a House Armed Services subcommittee.

Maine’s Bath Iron Works, a General Dynamics Corp. subsidiary, is building one Zumwalt, and Northrop Grumman Corp.’s Ingalls shipyard in Mississippi is building the other. Both shipbuilders declined invitations to participate at Thursday’s hearing.

The Navy’s decision to scrap its costly Zumwalt after the initial two ships are built has sparked a firestorm on Capitol Hill as some members, including Sen. Edward Kennedy, D-Mass., have threatened to block ship funding unless military officials can better justify their decision.

Rep. Niki Tsongas, D-Mass., pressed the Navy to explain its decision to stop buying more Zumwalts due to its latest threat assessment.

The decision was based on recent activity by potential adversaries, McCullough said, declining to be more specific during the hearing.

Subcommittee Chairman Rep. Gene Taylor, D-Miss., said while he has expressed concern about cost estimates for the Zumwalt, he did not recommend the program be canceled.

“If the Navy wants to build more of them, we need more information,” Taylor said. “Information not just about cost targets for new ships, but information on the total concept of support for the entire fleet of destroyers.”

The first two Zumwalt ships are expected to cost $3.2 billion each, compared with the $2.2 billion price tag for additional orders of the current Arleigh Burke, or DDG-51, destroyer. However, the cost of a DDG-51 is expected to fall to $1.8 billion in future years.

Critics have said they anticipate the costs would grow much higher on the Zumwalt, making it difficult for the Navy to build large numbers of those destroyers.

The Navy now hopes to build eight more DDG-51 destroyers, saying they have the capability needed to offer ballistic missile defense. Reopening the DDG-51 production lines also will be less risky than continuing the Zumwalt beyond the first two ships, service officials said.

To date, 62 ships have been authorized for the DDG-51 program. A total of 53 ships have been delivered to the Navy.

Both Bath Iron Works and Northrop Grumman have expressed concerns about getting the advanced materials needed to build more destroyers, but have assured the service they could restart DDG-51 lines in 2009, said Allison Stiller, Navy deputy assistant secretary of ship programs.

The Zumwalt was conceived as a stealth warship with massive firepower to pave the way for Marines to make their way ashore. It features advanced technology, composite materials, an unconventional wave-piercing hull and a smaller crew.