HISTORIAN Stephen E. Ambrose makes no bones about it: "I'm a hero-worshipper, and Meriwether Lewis is one of my heroes."
Ambrose has put his hero worship between the covers of a book titled "Undaunted Courage" (Simon & Schuster, $27.50). It's a departure for Ambrose.
After all, he's best-known for his work with 20th-century military heroes - as the leading biographer of Dwight Eisenhower, for example, and as a leader in the push to put Colin Powell in this year's presidential race.
But Ambrose has nursed an obsession with Lewis for two decades, ever since an aunt gave him a copy of the journals written by Lewis and William Clark, his partner on the expedition across the Louisiana Purchase to the Pacific.
And last fall, when Powell called Ambrose on the day after the general decided against an uphill charge in politics, the historian responded by citing his 19th-century hero and a predicament that occurred in June 1805.
"I told him about the day Lewis and Clark arrived at the point where the Marias joins the Missouri (near Great Falls, Mont.), and they weren't sure which river was which.
"Lewis had strict orders from Thomas Jefferson to follow the Missouri, but the Marias was in flood, and all the men except Lewis thought the Marias was the Missouri. They all said, `It's the right-hand fork.' But the captain said, `No, it's the left-hand fork.'
"The men replied, `We think you're wrong - but we'll follow you wherever you choose to lead us.'
"General Powell loved that story. And I think that in the year 2000, we're going to get him as president."
In a recent book-tour interview here (he also spoke at the Missouri Historical Society), Ambrose said that like the Missouri River itself, public interest in Lewis and Clark tended to rise and fall.
"Today, I don't think many Americans have any idea of the significance of their discoveries. But the farther west you go, the more people know. I was in Washington and New York last week. It was sad." He shook his head and repeated himself: "Sad."
Things have always been happier here. After all, Lewis and Clark set out from Wood River on May 22, 1804, and they considered their journey ended only when they stepped ashore in St. Louis on Sept. 22, 1806.
Ambrose said that Lewis would recognize nothing in today's St. Louis - "nothing except the Mississippi River, of course. It's still big, and it still has a lot of floating logs in it."
In his book, Ambrose describes the St. Louis of that era as a town on the make. In the interview, he said, "St. Louis was the most entrepreneurial city in America, or at least in the American interior.
"If people like Bill Gates had been around back then, they would have come to St. Louis. It was the Seattle of its time - a place where you could get rich quick.
"With $500 and a lot of luck in fur trading, you were looking at a profit of 400 to 1,000 percent.
"And remember - when Lewis left St. Louis in 1804, it had about 1,000 whites. When he returned in 1806, it had about 5,000. The place was just bursting with energy and …