The railways of Mexico conjure up cowboy film images -- mustachioed bandits robbing gold and silver bullion from freight cars or revolutionary hero Pancho Villa conquering the desert towns of the north with his armored train.

Today's reality is tamer and infinitely more comfortable. The night express from Mexico City to Monterrey, in particular, must qualify as one of the great trains of our time.

Every evening at 6 o'clock the Regiomontano (the Man from Monterrey) leaves the moders marble-lined (Word Illegible) station in the Mexicarr capital on its 15-hour journey to the main industrial center of Mexico far to the north near the border with the United States. The Regiomontano consists of half a dozen sleeping cars, a restaurant car, and a club or observation car which take travelers the 1,000 kilometers in considerable comfort at the modest price of between $20 and $30.

As the two diesel locomotives haul the train out of the station, the traveler is given a glimpse of Mexico City's startling mixture of the ancient, the ultramodern and the shabby. The line passes within a few yards of some of the city's most futuristic office blocks and a colonial church before it plunges into the northern suburbs, where naked children play around the disused railway carriages that are their homes.

As the Regiomontano picks up speed past the marshaling years filled with the freight cars of half the railway companies in the United States, Club Monterrey opens its doors and the regulars filter in to sip drinks or play dominoes around the stainless-steel bar. The rich farmland of the Valley of Mexico and the distant mountains go by while a gravely starched waiter does his rounds.

The regulars playing dominoes in the Club Monterrey, and indeed the passengers as a whole, are predominantly lower middle class -- junior government officials, say, or shopkeepers. The more monied Mexicans go between the two cities on the half a dozen airline flights that connect them daily or in their own or their companies' private jets.

The atmosphere is one of slightly seedy gentility -- after all, every passenger is treating himself to the luxury of a sleeping berth, an extravagance beyond the means of most Mexicans. The Regiomontano has definitely lost some of the glamor that it had 40 years ago, when it was the only fashionable way to travel between Mexico and Monterrey.

In the face of the decline in its social prestige, the Mexican railway hides its offended pride behind a facade of impeccable service funded in part, it must be admitted, from the generous subsidy that the federal government gives to its rail system. By 8 o'clock darkness has fallen and the restaurant car is buzzing with activity as the white-coated waiters scurry to and fro with one or other of the three set menus, the most expensive of which costs only the equivalent of about $3.

As the dinner service ends a few travelers return to the Club Monterrey for a nightcap and a chat before retiring for the night to their berths. The last of the world that anyone but the locomotive drivers are likely to see is the upturned face of a peasant peering from a serape at midnight from the station of San Juan del Rio.

As dawn breaks the Regiomontano is beginning to reach Saltillo, the last big town before the final destinantion. Over-night the landscape has changed from rich arable land upon which was based the wealth that helped create the great Aztec civilization, to the dry semi-desert of the northeast which produced nothing to rival the flourishing cultures to be found elsewhere in Mexico.

Where there is water the land turns a delicate pink with the almond blossom, but for much of the time the Regiomontano wanders through stony waste which supports little but cactus and sage. The villages are poor and isolated with names like Soleded -- Loneliness. Not that the traveler suffers. As the twin diesels head down the canyons and through the tunnels after Saltillo, he can be enjoying bacon and eggs and coffee as the restaurant car gets bank into its stride.

As 9 o'clock approaches, the suburbs of Monterrey, the ugly city of steel mills and glass works, rich familes with rightwing politics and bubbing discontent in festering slums, come into sight. For many people it will have been must better to have traveled to Monterrey than to have arrived.