Every year, millions of Americans plan bicycle trips, be it for touring or getting in shape or both. And whether they ride for a couple of days or a couple of months, they often come home shaking their heads and saying -- "Boy, I really hadn't anticipated that . . ."

How can you anticipate when and where your bicycle will break down? Or that your lunch will be squashed to inedibility by the tool kit packed next to it? Or that you'll run out of money before you reach your destination?

You have to hope for the best and expect the worst and consider yourself lucky if you make the trip unscathed.

I learned this during a 30-day, 3,000-mile trip across the country last year. There were many times that the trip just didn't seem worth it -- inching up five-mile hills in West Virginia, fighting 40-mph headwinds in Kansas, suffering from bronchitis in New Mexico.

But at other points, the trip was an unforgettably inspiring -- standing atop a 10,000-foot peak watching eagles below circling the cliffs, cycling through 100 miles of desert with only the sound of the wind to break the silence, or being invited for dinner at the home of someone you just met.

And it was definitely worth it when I rolled into Los Angeles 30 days after leaving the District. Going the distance can be one of the greatest experiences in life -- be it three miles or 3,000 miles.

"A lot of people who sign up for bicycle trips do it for the confidence," says Brannen Ulrick, 27, cooperative trips program manager for American Youth Hostels. "It sounds very intimidating when people hear about riding long distances and these people ask themselves, 'Can I do it?' It's a great feeling for them to cover the distance under their own power.

"Some of the best experiences are that you are treated differently when you're on a bike. Either people throw beer cars at you and yell at you or you're treated real well . . . Without even asking for help, they seem to want to go out of their way for you."

On a bicycle, he says, "you have the time to stop and talk to people, and you're not just passing through at 55 miles per hour. I heard a story about a girl who was traveling with a group through Ohio. It was her turn to cook and she didn't know what to cook. She told this to a woman who owned a bakery, and the woman and her daughter showed up at their campsite down the road later that evening with enough the food to feed the whole crew."

Three types of preparation are essential to a safe, enjoyable ride:

Physical. The more you pedal before the trip, the less pain you'll have during the trip and the better chance you'll have of finishing with happy memories.

"You don't have to punish yourself," says Hugh Johnson, a 27-year-old cartographer at the National Oceanic and Atmospheric Administration, who takes weekend and week-long trips. "Ride a few miles in the evening and a few miles on the weekend."

Even though Johnson is an avid cyclist, he encountered tendonitis on the eighth day of a 10-day trek through New England. "My knee gave out in the mountains of New Hampshire and the pain was awesome," he recalls. "It was raining, and the knees tend to go faster in the rain. I rode for two days of 50 to 80 miles a day through mountain passes, but I had to stop on the last day and my friend had to drive back and pick me up."

Consider weather and terrain you're likely to encounter on your trip and be sure you're physically prepared to ride in those conditions. Ride in the rain on some training rides and practice cycling hills. Pack appropriate rain gear, such as a light, breathable windbreaker, Gore-Tex jacket or waterproof, wool bicycling sweatshirt.

*Mechanical. Knowledge of bicycle repair and a supply of spare parts is crucial. "Mechanical problems never come at a good time," said Jim Roberts, a 32-year-old from Springfield who went cross country last spring. "One time, I broke down in the middle of the desert without shade. One time, I broke down in front of a post office in the drizzling rain. Both times, it was broken spokes. But if you are prepared, you can minimize the time and hassle of repairing your bike."

Flat tires and broken spokes are the major bicycle repair problems. Buy a good repair book, ask experienced bicyclist lots of questions and learn how to maintain your equipment. Bicycling magazine is a good source of information.

"I've been riding bikes since age 14," Ulrick said. "Either it's fixable and I can fix it, or it's broken and I need to hitch a ride in to town."

Psychological. The mental preparation you need typically has a lot to do with who your cycling companions are. I rode alone because I wanted to ride at my own pace, I wanted to stop when and where I wanted, I wanted to be directly responsible for completing the journey or not.

Roberts began his trip with a partner, but at the halfway mark, the two went their own ways because Roberts' partner needed to return to Washington by a certain date.

"Everyone should have an equal time frame," Roberts said. "One person shouldn't be required to get back at a certain time. Another thing is personalities. You should know how people are going to react to each other."

The best thing about riding together is that if there are any problems, there's someone to lean on. And there is safety in numbers.

"People that you seem congenial with, you find that when you get out there it isn't the case," said Ulrick, who leads trips of nine to 70 days around the country. "They have different expectations and different goals and different things they want to get out of the trip. You can have some heated discussions over the campfire at the end of the day."

All the energy and time spent planning the trip could be wasted if you aren't psychologically prepared for the inevitable hard times that lie ahead: the winds and the rain, the heat and the cold, the trucks and the mean people, and the agony and frustration of trying to succeed when at times it seems like nothing is going right. Concentration on the goal, and how good it will feel to reach it, can help.

Stick with it and be flexible when following an itinerary. The trip might not go exactly as planned, but then again, the challenge of successfully dealing with the unexpected can make the effort all the more rewarding.