Sierra Madre, Mexico — First, you have to understand that, with a good tailwind, this bus tops out at about 17 miles an hour. Then, consider that we are at least five miles from the train station; the train leaves in 20 minutes; and the bus driver is in the hotel lobby, arguing with a guest, as we sit huddled in the darkness of the bus, waiting to leave.
Anxiety begins to spread like the morning fog. The clock keeps moving in its relentless way until, at about 15 minutes before train time, I go into the lobby to suggest that the driver consider departing on his appointed rounds.
I arrive just in time to hear him say, ''Let's discuss it over a cup of coffee,'' as he takes the guest diplomatically by the arm.
''I can't,'' the guest answers with a helpless expression. ''I've got a bus to catch.''
''Don't worry. I'm the bus driver.''
Welcome to Mexico, and to the Ferrocarril Chihuahua al Pacifico, the famous ''railroad in the sky,'' the line they said couldn't be built, the ticket to Copper Canyon, which is billed as ''more spectacular than the Grand Canyon.'' Welcome to streaked windows, noisy coaches, and uncomfortable seats. Welcome to misrepresented train schedules and underquoted prices.
And, finally, welcome to three hours of the most spectacular, breathtaking mountain scenery you are likely to see this side of the Himalayas.
But it takes a while to get to the scenery.
Predawn in Los Mochis. A slender rivulet of rose light parts the horizon and the land in the distance. The bus groans into the station yard and we bundle out and hustle for the train.
Only, this isn't the train. The crowded coaches are filled with families, boisterous children, and a few pets. It is impossible to see out the windows. Certainly, this cannot be the ''VistaTren'' with its grand observation car, promised in the travel brochures.
Well, it turns out after a day of waiting in Los Mochis that the vista train hasn't run for six months - although the woman in the local travel office swears it has been more like 10 years. It turns out also that every Tuesday (from Chihuahua) and Thursday (from Los Mochis), a second-class train runs on this line. If you want to travel in any kind of comfort with any kind of visibility, you'd better go on other days.
No one tells you this. But then again, no one tells you anything.
A number of vacationers are miffed, for instance, to find out that the bus fare to and from the train, airport, and hotels is not included in the package price, as they were told by their travel agents. This is only the first of many small surprises they will encounter along the way.
In the travel Olympics, the journey to Copper Canyon rates a reasonably high ''degree of difficulty.''
We're not talking about crossing the Alps on an elephant here. But neither are we discussing the whisper-soft transit of a high-speed Japanese train. The Chihuahua al Pacifico's trek through the Sierra Madre, and the recommended stopover at Copper Canyon lodge, should be considered only by those who like their travel medium-rugged and their scenery awesome and majestic.
We are rolling through the flat, irrigated fields of the rich Sonora Valley and up into the bristling, scrub-arid earth that leads to higher ground. All the while, the Sierra Madre grow more prominent and dignified.
As we approach the longest span in the journey, three girls are singing Mexican melodies on the platform between cars.
Quite suddenly, after the unimpressive bridge, we are pouring through wild country with strange, stark trees that bear tiny white blossoms. A huge promontory of rock rises out of the earth, all gnarled and ancient. We are coming into the mountain country.
The high mountains loom around us, giving the first intimation of how awe-inspiring this thing will get.
And, then, the bridge. A slender, lofty structure with spindly legs, it bears this old train across a sheer drop and the tiniest ribbon of a river. Before long, we are winding our way through towering promontories covered with dense tree growth and topped by thick slabs of rock.
Gradually, the train works its way back into country that is as forbidding as it is beautiful. On each side of the railbed rise sheer faces of rock and trees. We are in the kind of world that speaks staggeringly of the earth's formative forces. One vista after another comes sliding into view: the endless escarpments , occasionally dangling slender falls, that drop incredible distances.
After a while, you can only grow quiet and amazed at the continuous majesty of country so profound and still. The passengers, Mexican and American, young and old, are pretty well struck dumb by the view.
After rolling through some open ranching country, the train comes into the kind of terrain traversed by Walter Huston, Tim Holt, and Humphrey Bogart in John Huston's ''Treasure of the Sierra Madre.'' All shale and bleached stone peppered liberally with dark, hardy trees.
Nothing that happens from now on begins to compare with this first leg of the journey, which is why many smart travelers take the train only as far as Creel, spend a night or two, and come back the same way without ever traversing the second half of the 12-hour journey. This makes a lot of sense, because from here on this railroad becomes just another ride through Mexican mountains.
This is not to denigrate the Copper Canyon. Big, deep, august, it yawns into forever with its vistas and distances. But it is not, as many American tourists grumble, any Grand Canyon. It is not nearly so awesome as what we just went through.
Before we hit Creel, the train finally climbs into the high mountain country, cold clear, and above the world's sordid tumult.
So it's possible to dream of lofty things, until you get into Creel and onto the ''modern, spacious'' bus, which turns out to be a late-'50s vintage tub that saw its last shock-absorber change a decade ago.
Copper Canyon Lodge consists of a string of conjoined log cabins with wood-burning stoves (one room has a fireplace) and no electricity. It sits in a shallow basin of land surrounded by ridges and high silence. Within easy walking distance, you'll find a magnificent waterfall and enough solitude mingled with mountain wildness to fill your mind for an afternoon.
You can supposedly find caves with Indians, if you are willing to ride on horseback for eight hours to get to the bottom of Urique Canyon. Be warned, however, that two young men set out on this tour one morning and turned back half an hour later realizing they were not up to it.
For those who remain close to the lodge, there is always a walk around the nearby environs, a game of pool, or an effort to talk with the highly taciturn Indian help.
I took a walk and thought about the relative value of this trip.
What I came up with was this:
The Copper Canyon is not cheap. And while the high country and rugged outdoors it offers are impressive, they are hardly unique. I don't think I would do it unless I were already in this part of Mexico. And then I'd check the ever-changing schedules, phantom prices, and availability of suitable railway equipment.
But I don't think I'd ever feel really sure about the whole thing.
Since many of the railroad people, hotel clerks, and others speak only Spanish, it is wise to work through a travel agent; but wise, also, to make sure the agent takes certain precautions. For instance, do not rely on Hoteles Balderama to make your train reservations. Have the agent call the Ferrocarril Chihuahua al Pacifico directly and ascertain exactly when the first-class train runs. Also, double- and triple-check reservations once you arrive.
The costs will fluctuate, but a current breakdown is as follows (prices for a single first, then a double): train - $11.35, $23.10; hotel in Los Mochis and Chihuahua, $45, $60; ground transportation (cabs, buses), $7.50, $12; Copper Canyon Lodge (including meals), $40, $85; meals, $20, $40. Grand total: $123.85,