I sort of compare it with what mothers must feel when they send their sons off to war. It's a totally unknown thing," observes Patricia Duncan of her sons, David, 24, and Donald, 22. "But there is a point where you do have to let them go."

Where the Duncan brothers were going was on a 16-country bicycle tour around the world. Setting out with them from Washington, D.C. last December were Jim Logan, 32, from Norman, Okla. and Dave French, 33, a Virginian (who has since dropped out). Several weeks ago, at their midway point in India, the surviving trio were hardly winded and bidding well to reach their goal of returning to their starting point by Christmas 1982.

Whose idea was this, anyway? "Mine," admits David Duncan. "I was sitting around at Vassar College, my alma mater, eating a hamburger with my track coach. I said I would like to see the world, and that it might be fun to bicycle because that's a good way to see it. He gave me the idea of hooking up with a charity in order to raise money. It would add a purpose to our wanderings."

That was more than two years ago, but the Kansas City Duncans are not the sort to turn away from a challenge. Dave and Don are sons of Herbert Duncan, a former national director of the American Institute of Architects. Dave's credits include composing and performing as a folk guitarist, a bit of acting in the 1975 TV remake of Friendly Persuasion, and a summer hitch as an aide to U.S. Sen. John Danforth of Missouri. Don is a graduate of Maine's Bowdoin College and, like his mother, an accomplished photographer. The brothers also have a physician uncle who served with Project HOPE, the nonprofit international health-care foundation, so the choice of charity came easily. Thus the enterprise officially dubbed World Bike for HOPE was born. Object: to get contributors to pledge so much per mile ridden toward the overall goal of raising $500,000 for HOPE. Meanwhile the $50,000 cost of the expedition—equipment, supplies, traveling money—is being borne by some 40 private and corporate sponsors, including American Express, Pan Am, Hallmark and Fuji, which is providing the group's 18-speed bikes.

After flying to Madrid, the quartet pedaled for 3,000 miles through Spain, France, Italy and Greece before flying on from Athens to Tel Aviv for a Mideast tour of Israel, Egypt and Sudan. The novelty of the trip quickly wore off, they found, but not their enthusiasm. "I cannot think of a better way to experience fully all the sights, smells, sounds," Don wrote his parents. "Little things are a delight; a man whistling in the street, church bells ringing in a small hilltop village, the sea and the smells from homes."

Though none of the bikers are linguists, they've gotten on with the locals so far by gesturing. One night near the Gaza Strip they were rousted out of their sleeping bags by an Israeli patrol. "I don't know if they thought we were terrorists or what, but it's disconcerting to have M16s pointing at you," reports Dave Duncan. After convincing the soldiers that they were friendly, the travelers spent the rest of the night at a hospitable kibbutz.

Averaging about 50 miles a day, they have encountered no major problems but plenty of minor annoyances. Each bike carries 125 pounds of equipment and food, and headwinds have proved testing. As Logan notes, "There are no downhills in the wind." In the 120-degree heat of Sudan, camping equipment dried out and shrank, bike tires burst (Jim had 10 punctures in "about five minutes," he says). Occasional loneliness turns into cravings for hamburgers and milk shakes. In the Nile Valley viral lung infection forced David French to end his ride and return home. The others caught a plane from Port Sudan to Pakistan for the Asian leg of their journey.

This month they arrived in Bangkok and are heading for Singapore, the Philippines, Hong Kong and Japan. Of all their experiences, the most affecting, they say, has been encountering refugees—Palestinians, Eritreans, Afghans. "We were not used to these things at all," Dave says, "but now it's very real to us—a tragedy."

So far the travelers haven't raised much money for HOPE. They will begin canvassing for funds in earnest in September with their 3,000-mile bike-a-thon from California across the Sun Belt to their starting point. En route they will solicit pledges to HOPE based on their total mileage or on completion of various legs of the tour. "Right now we are establishing our credibility," says Jim Logan. Can they go all the way? "We know we can conquer the bicycle and survive," he replies confidently. "It's our Midwestern streak. Stubbornness gets us through."