President Carter interceded yesterday to head off a strike by 2,500 train dispatchers that could have shut down most of the nation's railroads later this week.

Acting under the Railway Labor Act, Carter created an emergency board to investigate the dispute, effectively postponing any strike action for at least 60 days.

The American Train Dispatchers Association (AFL-CIO) was the lone holdout among 13 rail unions in reaching a new 39-month contract with the National Railway Labor Conference, which bargains for most of the nation's railroads.

The dispatchers union is the smallest of the group but could shut down the railroads by throwing up picket lines that would be honored by other unions representing more than 500,000 rail workers.

Under complicated procedures of legislation governing contract bargaining for the railroads and airlines, the union would been free to strike at 12:01 a.m. tomorrow if the president had not intervened by appointing an emergency board.

Creation of the panel was recommended by the National Mediation Board after it declared an impasses in the negotiaions last month.

The panel will have 30 days-or longer if the president deems it necessary-to investigate the dispute and make recommendation for a settlement. Then another 30 days are allowed for negotiations based on the group's findings. After that, the union would be free to strike unless Congress moved in and imposed a legislated settlement.

The three-member panel will be headed by James J. Reynolds, who was undersecretary of Labor in the Johnson administration. The other members are Ida Klaus, a New York labor arbitrator, and Nicholas H. Zumus, a Washington arbitrator.

According to B.C.Hilbert, president of the Illinois-based disparchers union, the bargaining deadlock was primarily over work rules, including the union's demands for a paid meal period, revised disciplinary procedures and travel pay improvements.

He said there was no dispute over the industry-wide wage and benefit settlement, which calls for increases of about 35 percent over the 39-month life of the contract, dating back to Jan. 1. 1978. The cost exceeds the government's 7 percent guideline for are exempt because they are based on a pattern set before the guidelines took effort last October.

Hilbert said a strike date would have been scheduled Thursday if the emergency board had not been empaneled, and it was expected that the walkout would have been honored by the other unions. He said it would have affected 80 to 90 percent of the nation's rail freight traffic, excluding only the Conrail network, the Union Pacific, the Illionois Central Gulf and the Amtrak passenger rail service.