TO American Indians living in New England, it must have seemed a wondrous transformation: the green leaves of summer slowly turning brilliant shades of red, orange, and gold as autumn tiptoed in. In this neck of the woods, Indian legends abound to explain why the trees turn and what the change symbolizes.
There is also a scientific explanation: The warm days and cool nights of early fall produce a corky substance that blocks the flow of water to leaves. The chlorophyll in the leaves breaks down, and the sugar that remains produces the vibrant colors that ''leaf peepers'' relish.
Science or legend, it's hard not to be moved by the vibrant colors of autumn. And judging by the hundreds of thousands of tourists who pass through each September and October, New England is an ideal location to witness this seasonal change.
Some leaf-peepers come by bus or car, armed with maps and an itinerary, and stay for a week. Some set out on spur-of-the-moment day trips, and wander back roads. Still others view the foliage from the seat of a bike, the bow of a canoe, or even from a hot-air balloon.
The key, of course, is timing. When the leaf colors peak depends on a number of natural factors, as well as locale. In Vermont, the last week of September and the first week of October are usually the best for leaf-peeping. In the vast state of Maine, the north typically peaks the second weekend in September, while the southern portion is at its best the second weekend of October. In Massachusetts, the more mountainous areas in the west, such as the Berkshires, turn first, usually in early October.
'THE advice I'd give would-be leaf-peepers, especially non-New Englanders, is to plan an expedition for longer than one day because the weather can change so quickly,'' says Ray Wiggers, a botanist, traveler, and author of ''The Plant Explorer's Guide to New England'' (Mountain Press Publishing Company, 1994).
Mr. Wiggers, a native Midwesterner, set out to explore New England while he was living here several years ago. His goal was to learn about the wild-plant community, but along the way he discovered that the region's diversity, climate, and compact size all add up to a leaf-peeping experience unrivaled by other regions. In his book, Wiggers maps out 54 tours of the area, 18 of which are specially recommended for viewing fall colors.
''I fumbled my way around the states,'' Wiggers says. ''Eventually, I could connect the dots.''
For colors ''at their crispest,'' he recommends a 70-mile Vermont route from Barre to Rutland. [See map.] In New Hampshire and Maine, Wiggers directs leaf-peepers on a 120-mile tour from Wolfeboro to Sebago Lake State Park. And in Massachusetts, he suggests an 18-miler from Northampton to West Chesterfield.
Wiggers says one of his first discoveries about leaf-peeping in New England was that the ''southern'' states have a lot of good fall-foliage sites. ''You don't have to go to the White Mountains of New Hampshire to see great color,'' he says.
He admits, however, that the farther north a leaf-peeper travels, the more northern hardwood trees he or she will find. ''The colors of the northern hardwoods - sugar maples, for example - punch out above all the rest,'' he says.
Wiggers traveled by foot and by car. Others choose to see the trees by boat, train, or even ski chairlift. In Maine, whitewater rafting companies have traditionally been booked only during July and August. ''Now more people realize it's just as good to come in September when the water is still warm, there are fewer people, and the foliage is beautiful,'' says Nancy Marshall of the Maine Office of Tourism.
Ms. Marshall says Maine is a less-traditional destination for leaf-peeping than New Hampshire or Vermont, but it is no less dramatic. And there's a bonus: As no-vacancy signs go up at inns and motels across much of New England, travelers typically have little trouble finding a place to stay in the less-crowded Vacation State, she says.
Leaf-peepers also can be assured of knowing exactly what they're in for. Jamie Cope, information officer at the Vermont Department of Travel and Tourism, calls 15 foresters throughout the state twice a week to find out where the colorful trees are, how intense the color is (golds and deep reds or just blushing), whether there's been rain, and how many leaves are left.
''They even tell me about specific stands of trees,'' Ms. Cope says. ''They'll let me know if a stand of trees is especially brilliant along Route 100 to the left of a particular pond.'' She records the information for the state's leaf-peeping hotline.
In the Berkshire Hills of Massachusetts, an area Wiggers says ''is always good'' for fall foliage, leaf-peepers may do more than look. ''People like to be involved,'' says Abbie Goodman, director of the Massachusetts Office of Travel and Tourism. That explains all the fall-foliage festivals in the area.
At the end of September, for example, there's a week-long fall-foliage festival in North Adams. There's also a harvest festival at the Berkshire Botanical Garden and a special autumn weekend at the Hancock Shaker Village.
Steven Ziglar of the Berkshire Visitors' Bureau describes the area's fall atmosphere as ''more laid-back'' than the summer's busy days. The festivals and other activities keep people busy, he says, but the color is the real draw.
''The Berkshires have both hardwoods and softwoods, with maple trees of every description,'' Mr. Ziglar says. ''What makes it unique is the diversity of color and the large lakes with trees reflected in them. The vistas are gorgeous.''
No matter what state one visits and regardless of the mode of transportation, travel experts all advise planning ahead and booking reservations early. Then again, travelers can always do as Wiggers did: Take a chance on the weather, forget about reservations, and simply wander back roads, connecting the dots as they go.
''You could even take the same fall-foliage tour 50 times, and you'll see something different each time,'' Wiggers says. ''That's what's so compelling about New England.''