The first Acela trains, which Bombardier made with France's Alstom SA, went into service in 2000. Amtrak is to announce the new supplier this spring. Alstom declined to comment on whether it is bidding.

A request for proposals closed Oct. 1, but Amtrak has not made the identities of the bidders public. The railroad is looking to buy 28 trains, up from 20 last time, with capacity for at least 425 passengers, up from about 300.

Bombardier spokeswoman Maryanne Roberts said Amtrak changed its technical specifications during the proposal stage.

"Unfortunately, the time remaining before the due date for the technical proposals was not sufficient for us to make the necessary adjustments to our proposal," she said in an e-mail.

Amtrak did not immediately respond to requests for comment.

The Acela Express service, which runs from Washington, DC to Boston through New York, was hit by mechanical issues in its early years. The relationship between Amtrak and the Bombardier/Alstom venture soured, and both sides sued before settling in 2004.

Even so, Bombardier had said previously that it was interested in the new Acela, and analysts said the Canadian company would have a good shot at the contract.

Bombardier and Alstom were paid $730 million for the original Acela trains and their maintenance facilities, plus more for maintenance contracts.

Problems with the first Acela trains were legendary in the railroad industry. Bathroom doors malfunctioned and small cracks appeared in key parts. In 2005, Amtrak idled the whole fleet for months after discovering cracks in brake discs.

A spokesperson for Hyundai Rotem said the Korean company had submitted a letter of intent to bid.

Siemens AG declined to comment on whether it is bidding but a spokesman said it has "great interest" in the United States. It has a manufacturing facility in California.

State-backed China CNR Corp has teamed up with SunGroup USA to bid on a California high speed rail project. A SunGroup spokesman said the consortium is not bidding on Acela. CNR did not immediately respond to queries about whether it is bidding, and rival CSR Corp declined to comment.

(Additional reporting by Hyunjoo Jin in Seoul, Thomas Wilson in Tokyo, Natalie Huet in Paris, Maria Sheahan in Frankfurt and Brenda Goh in Shanghai; Editing by Dan Grebler)

By Andrea Hopkins and Allison Martell