Amtrak President George Warrington is resigning to become head of New Jersey's bus and rail agency, a surprise move that comes as the financially troubled national passenger railroad fights efforts to break it up.

Warrington will stay on at Amtrak until an interim successor is named, an Amtrak source said Wednesday, speaking on condition of anonymity.

Warrington, 49, has led Amtrak through a difficult four years during which it tried to end its three-decade reliance on operating subsidies from the federal government.

Warrington's strategy was to grow the railroad to fiscal health, but costs rose along with income and ridership. Watchdogs now agree it will not achieve self-sufficiency by the December deadline set by Congress.

The source said no timetable has been established for Warrington's departure but that Amtrak's governing board already has a short list of potential successors.

Amtrak spokesman Bill Schulz declined to comment when asked if Warrington was leaving. Warrington could not be reached.

In becoming executive director of NJ Transit, Warrington will return to his roots. A native of Bayonne, N.J., he served as deputy state transportation commissioner before joining Amtrak.

NJ Transit carries 400,000 bus and train riders each day, making it the third-largest mass transit agency in the nation behind New York and Chicago.

Michael Dukakis, the former governor of Massachusetts who now serves as vice chairman of Amtrak's governing board, said in January that Warrington had assured the board he would stay through the end of 2002.

"This has been a very tough job, and he's been terrific," Dukakis said at the time. "There isn't a single person on the board who isn't a Warrington fan."

Warrington took the job a year after Congress set the deadline for self-sufficiency and appointed the Amtrak Reform Council to monitor progress. Last month the council sent to Congress a plan suggesting the government break up Amtrak and open passenger rail to competition.

Warrington responded by saying the railway needed $1.2 billion next year -- twice what it received this year -- and threatened to cut some or all of its 18 long-distance trains unless it receives that amount. He also trimmed 1,000 of the company's 24,600 jobs and made other cuts in training, advertising and equipment maintenance.

In a speech last year, Warrington appealed to political leaders to resolve whether the railway's chief mission is to provide national passenger service -- including running certain politically popular but financially ill-advised long-distance trains -- or to break even.

"For 30 years Amtrak has been expected to perform like a business and at the same time serve community needs like a nonprofit organization. We cannot do this," he said.

Warrington, who took over as Amtrak president in December 1997, presided over the introduction of the nation's first high-speed train -- the amenity-filled Acela Express that runs between Washington and Boston and hits a top speed of 150 mph. He began a frequent-traveler rewards program and a customer-satisfaction guarantee. And he asked Congress for $30 billion over 20 years to close what he calls a "rail investment gap."

Under Warrington, Amtrak also aggressively sought new business opportunities to supplement its revenue from passenger trains.

He named a vice president to oversee development of Amtrak's real estate holdings -- including land around stations in Baltimore, Philadelphia and Chicago -- and Amtrak's first director of merchandising to develop and market company-branded souvenirs.

Amtrak won federal approval in 1998 to carry time-sensitive packages and freight shipments and now transports packages, periodicals, dry freight -- even fruit in refrigerated cars from West Coast to East.

Two years ago, Warrington introduced a plan to add new passenger routes. Though designed in part to expand package-delivery opportunities, the plan promised to bring trains to the neighborhoods of 4 million potential new passengers. But virtually none of the 14 specific proposals to extend or add routes has panned out.

Kenneth Mead, the Transportation Department's inspector general, reported in January that Amtrak lost $1.1 billion in 2001, the most in its 30-year history, and had made no progress toward becoming financially self-sufficient.

Amtrak was created by Congress in 1971 to take over the passenger rail operations of private railroads. Today, it serves more than 500 communities in 46 states over a 22,000-mile route system. The railroad carried a record 23.5 million riders in 2001.