Amtrak (search) will not be able to run any of its high-speed trains until the summer because of delays in getting replacement parts to correct brake problems on Acela Express cars, railroad officials said Wednesday.

"The earliest you'll see trains back in service will be sometime in the summer and then you'll see a gradual return," said Amtrak's chief executive officer, David Gunn (search). "What will control that is the availability of parts and the speed in which they come, and the time it takes to put them on."

Before Amtrak's showcase service resumes, Amtrak's chief operating officer, Bill Crosbie (search), said there must be agreement on how long the new brakes will last.

The brakes were to last 1 million miles; the current Acela fleet had about half of that mileage.

Amtrak pulled all of its 20 Acela (search) trains out of service on Friday after finding millimeter-size cracks in 300 of the fleet's 1,440 disc brake rotors. Each Acela train has 72 brakes.

"This part is unique to the Acela and there is no active production line casting them," said Crosbie said. "The manufacturer has told me this will take some time."

Crosbie said there are fewer than 70 disc brakes available now.

Starting Monday, Metroliner trains — slower than Acela but faster than regular trains — will operate 13 of the 15 Acela round trips between New York and Washington.

Between New York and Boston, regular trains will cover nine of the 11 Acela round trips, Crosbie said.

Starting May 2, Metroliner trains will operate 14 of the 15 Acela round trips between New York and Washington. The New York to Boston Acela route will be operated by four Metroliner trains and seven regular trains, Crosbie said. Amtrak pulled trains from across the country to fill in for the Acela runs.

Bombardier, Inc., the Montreal-based company that builds the Acela trains, has only 80 disc brakes in stock, the company said. Alstom SA of France also makes the trains, and both companies were working on a delivery schedule with brake suppliers providing the replacement parts, Bombardier spokesman David Slack said this week.

The brake problem surfaced when a Federal Railroad Administration worker performed a routine inspection April 14 after a high-speed run to test whether Amtrak could speed up the Acela trains slightly on curves between Trenton and Newark, N.J.

On Monday, Amtrak put one Acela train back in service for a New York-to-Washington run, but the train did not make a scheduled trip from Washington to Boston because the wheels did not match perfectly.

President Bush is urging Congress to eliminate Amtrak's operating subsidy and privatize it.

A Senate subcommittee planned to debate Bush's proposal Thursday. The current budget gives Amtrak about $1.2 billion in operating subsidies and capital investment funds.

Acela normally makes up about one-fifth of Amtrak's service along the Northeast corridor, carrying an average of 9,000 riders on weekdays.

Acela Express began operating in December 2000 and was billed as Amtrak's answer to high-speed rail. The trains run only along the Northeast corridor, with top speeds of 150 mph. Acela trains can get from Washington to New York City in two hours and 48 minutes, while its regular fleet takes more than three hours.