Train buffs had better book passage now for a superscenic railroad trip - on TV. The Gulf/National Geographic Society television specials constitute one of the most dependably informative series on PBS. Like the magazine whose name it bears, the series is most often determinedly, but not deadly, serious. It usually manages to engage audiences with the thrill of intellectual revelation.
Every now and then, however, both the magazine and the TV show slip in a topic that is almost pure entertainment with only a pretense of the scholarly approach. Love Those Trains (PBS, Wednesday, Feb. 8, 8-9 p.m., check local listings for premiere and repeats) is one fine example. If you climb aboard, expect nothing but pure fun.
To the constant refrain of ''Chattanooga Choo-Choo,'' this loving look at trains and train people is a choo-choo buff's paradise. The viewer's ride on ''Love Those Trains'' includes meetings with train-hopping hoboes, up-to-date information on today's rail business, visits to private railway clubs, old photos and antique film footage of vintage trains, memory trips through the High Sierras, a few minutes on the legendary Durango-Silverton line in Colorado, and, finally, a seat on the newly refurbished Orient Express, where for a mere $5,000 you can take the five-day journey between Paris and Istanbul.
''Cowboy hats are out; engineer hats are in,'' says a woman to a fellow traveler on the Durango-Silverton express along the edge of the Animas River Canyon. Well, with half a million people working on the railroads, with renewed interest in rail travel, and with the rediscovery of the grand adventure that is railroading, not only the hats are in, so is rail travel itself.
Maybe even TV shows about it, too.