Washington ? Facing a possible strike that could have stranded hundreds of thousands of commuters, Amtrak reached a preliminary deal Friday that apparently heavily favors the railroad’s nine unions, who have worked for years without a contract.

The tentative contract includes back pay totaling more than three times what Amtrak was offering and none of the concessions on work rules that Amtrak had been seeking, said Joel Parker, a spokesman for the Transportation Communications International Union and a lead negotiator.

While the month’s-end strike was considered unlikely, the mere prospect of it had regional rail services across the Eastern Seaboard scrambling in recent days to put backup plans in place.

“We have averted a possible strike that could have had a crippling effect on the lives of millions of Americans,” Amtrak President and CEO Alex Kummant said in a news release.

Details of the agreement will not be released until it is ratified by affected union members in the next several weeks, according to a statement from Amtrak.

People familiar with the labor agreement, some speaking on condition of anonymity because the details had not been formally announced, said it adopts the recommendations of a presidential emergency board report issued Dec. 30.

The board’s report, which recommended that Amtrak grant back wages to its workers, triggered a 30-day countdown until a strike became legal.

Included in the deal are wage increases that average 35.2 percent over the life of the agreement from January 2000 through Dec. 31, 2009 – or about 3.1 percent per year, said W. Dan Pickett, head of the Passenger Rail Labor Coalition, who was involved in the deal.

Amtrak spokesman Cliff Black said there appears to be a “pretty universal feeling” that the agreement will be ratified.

If Amtrak workers had walked out for the first time in the railroad’s 36-year history, the 71,000 people who use the service every day would not have been the only ones affected.

Hundreds of thousands of people who ride commuter trains also would have suffered because many such services depend on Amtrak employees or infrastructure, particularly in the Northeast.