Travelers depending on trains to get home for Christmas vacation should expect a "very severe" crowding problem, an Amtrak official said yesterday.

James Bryant, a spokesman for Amtrak, said that even a 25 per cent increase in seating capacity at Thanksgiving was not enough to alleviate the overcrowding that resulted from people who decided to travel by rail because of gasoline shortages.

Bryant said Amtrack would "get every car we have on the tracks." He said the extra cars would be attached to existing trains.

The air travel situation looks particularly grim for the Christmas holidays because of the strike at Trans World Airlines and public uncertainty about air travel. Airline officials, though, are promising air service at the same level as last year.

William Sullivan, duty manager for the Penn Central office in Boston, said that the few first class seats on trains which can be reserved will probably be sold out by early next week.

Trains which will probably be sold out first are the 4:20 and 10:30 p.m. Boston-to-Washington runs.

No Shortage of Buses

The other alternative to flying, the bus lines, report no such problems. Nathan Karp, terminal manager for Greyhound Bus Lines, said that if buses are filled, "we just send another bus." He said that he anticipated no delays or shortages of buses.

Bryant said Amtrak expected the "heaviest crush" on the runs between New York, Philadelphia and Washington. He said that travelers still hoping to reserve seats should do so immediately.