The federal government yesterday approved a $139.7 million loan guarantee that will allow a Hawai'i company to move forward on plans to begin an interisland ferry service by April 2007.

The approval by the federal Maritime Administration came in Washington, D.C., as part of a $210 million financial closing agreement signed by the Hawaii Superferry, investors and the government, said Susan Clark, a spokeswoman for the Maritime Administration.

Under the agreement, the government promised to guarantee 78.5 percent of the estimated $178 million cost of building two high-speed passenger and vehicle ferries that will be used to transport passengers between Honolulu and Maui, Kaua'i and the Big Island.

The financial closing will allow the ferry company to move forward more quickly with its efforts, including hiring the first of about 300 expected employees and developing detailed operational plans for each harbor, Superferry officials said.

"Hawai'i is a big step closer to ending its long standing as the only archipelago in the world without ferry service between its major islands," company President Tim Dick said yesterday.

The first of the vessels, which can carry up to 866 passengers and 282 cars, is being built by Austal USA in Mobile, Ala., and is expected to arrive in Honolulu in early 2007, Superferry officials said. The second vessel, which will allow initial service to expand to Hawai'i County, is expected in 2009.

The company has said its passenger rates will be about half the current price of an interisland airline ticket.

The loan agreement was signed under part of federal law that provides government construction and financing guarantees for ships built and used in the United States.

The financial closing, which included a $71 million investment from a group led by the private equity firm of J.H. Lehman & Co., comes on top of a memorandum of agreement the ferry company signed with the state last month. Under that agreement, ferry officials agreed to pay the state a minimum of $2.3 million a year to use the harbors. The company also will pay state harbor usage fees and the 4 percent general excise tax. The state is providing about $40 million in barges and other equipment that will be used by the ferry operation.

The agreement with the state also requires Superferry to provide more detailed operating plans and studies on such potential problems as traffic and environmental concerns before it begins service.

"We will continue to meet with community members as we complete work related to the construction of our vessels and prepared detailed operational plans for our service," said John Garibaldi, the company's chief executive officer. "We are also in the process of establishing a board of advisers for each island."

Reach Mike Leidemann at mleidemann@honoluluadvertiser.com.