It is a mid-October morning and you are driving south on Massachusetts Avenue. All the way along your route to work a feeling's been building up inside and suddenly, as you cross the bridge over Rock Creek Park, you have a name for it: autumn.

For once in your life you wish traffic would come to its predictable halt. You want to stop and look at the view. The melancholy that melts a "fall person" - who finds spring too flashy - fills you. You resolve to visit New England as an autumn pilgrim some year, but fall's best beauty is fleeting, and your city-dweller's life presses in on you.You can't get away.

But you can.

Horticulturists agree that the best fall color show in the world happens on the eastern seabord of the United States. Many lovely vistas are less than a two-hour drive from Washington.

Leaves are starting to turn now. With only slight qualification, tree huggers predict colors will be most vibrant starting Oct. 15. ("Tree huggers" is what rangers assigned to the Washington area call themselves, as distict from "tree fuzz," the U.S. Park Police.)

If you want to leaf watch this three-day weekend, go north. The beautiful Pennsylvania countryside north of Williamsport is little more than four hours away. Western Maryland's Garrett County promise a galaxy of colors, especially along scenic Route 135 that passes mountains, lakes and state forests.

For a fall pilgrimage nearby, you naturally think first of the Skyline Drive in Shenandoah National Park, Va. and then of the traffic jam resulting when everyone think of it at once. Asst. Park Superintendent Bill Loftis says the traffic "isn't that bad. About the only kind of trafic jams you get is what we call deerjams , when people see a deer and stop their cars." A lesser-known but similar phenomenon is the "bearjam."

As for an exact date for high colors, the park has had a dry summer, the rains in September, "so no one is willing to say what that's going to do." Their best guess is the weekend of Oct. 15.

The winding drive is 105 miles long, from Front Royal, Va., south to Rockfish Gap. People who can't maneuver curving roads and gaze at views simultaneously might try taking in the splendor by driving Interstate 81 to the west of the Blue Ridge. The north end of the drive, about 60 miles from Washington, can be reached by going west via Interstate 66 to Route 55 leading to Front Royal. Front Royal's annual Festival of Leaves is Oct. 15 and 16.

Closer to home and ofteh overlooked in favor of its more famous sister, is a national park near Quantico, Va. The most impressive thing about Prince Wiliam Forest Park, during a visit two or three weeks before the height of autumn, is the silence. Sunday afternoon and you can walk on the main road. A car or park maintenance truck passes by, say, every 10 minutes.

Rangers there rate it every bit as beautiful in autumn as Shenandoah, without the overlooks and panoramas, but fewer tourists. A 35-mile network of marked trails weaves through the park, past a beaver pond or a stream stocked with trout. Prince William Forst Park is 32 miles southwest of Washington, a straight run down Interstate 395 and on to 195 south. A fall color walk scheduled for Oct. 15 starts at park headquarters at 2 p.m.

For a change of scenery, there's Elk Neck State Park on a peninsula at the north end of Chesapeake Bay. Although winter generally comes later to the coastal plain, the color will peak there, too, in mid-October if nights continue cool. The park offers campsites, rowboats and bicycles for rent, and crabs to catch. (Alas, the crab catch is low because of the big "die-off" in last year's cold winter.)

To reach the park, 100 miles from Washington, go north on Interstate 95 to the North East, Md., exit. Turn right onto Route 272, south to the town of North East and continue 10 miles to the park.

Farther west, northern Frederick County is blessed with three notable parks. There are scenic overlooks in Gambrill State Park, off Route 40, six miles northwest of Frederick. North of Frederick via Route 15 is Cunningham Falls State Park, noted for its 40-foot waterfall and its 42-acre lake.

Northernmost of the three is Catoctin Mountain National Park, also on Maryland Route 15, 65 miles from Washington.

The foliage target weekend of Oct. 15 and 16 coincides with the Catoctin Color Fest, an annual event sponsored by neighboring towns. In Thurmont, the center of the activities, a flea market will be operating along with two craft areas where 150 craftsmen will demonstrate and sell products such as painted porcelain miniatrues, pottery, woodworking, leather and wool. Other small communities nearby, such as Sabillasville, Rocky Ridge and Lewistown, will offer church suppers, chicken barbeques, craft shows and apple butter boiling demonstrations.

For all the parks, take Interstate 270 north to Frederick. From there, for Gambrill park take Route 40. For Cunningham Falls take Route 15 to park entrance. For Catoctin, take Route 15 north to Thurmont exit. Drive to Thurmont, then west on Route 77 about 3 miles to park entrance.

The final view in our foliage panorama sweep is, like all autumns and endings, a sad one.

It's only 30 miles north from Washington to Sugar Loaf Mountain, a privately owned park you can visit free. Leaves are starting to change there. But so is the scenery.

A toddler can scale the steps to the summit, and looking to the west you can see, on a clear day, the Blue Ridge 25 miles away. You can see where the Monocacy and Potomac rivers meet - at the Dickerson power plant. There, Pepco is just finishing construction on a smokestack 700 feet tall - almost two-thirds the elevation of the mountain you're standing on.

Bob Hollond, the park superintendent, says when he first came up here seven years, ago he could see the Washington Monument. But now urban smog obscures it. Late at night, after the park is closed, he comes up here, and, he says, he can see the lights of Gaithersburg. "It's changing," he says."So many more lights now."

Sugarloaf can be reached by traveling out Interstate 270. Exit on Route 109 west, then right in Comus onto Route 95, 2 1/2 miles to the mountain.

What causes leaves to change color? It's a tree's way of preparing for winter. The leaf's aging process is accelerated as nights grow longer, water is harder to draw from the ground and temperatures cool. Leaves of poplar, linden, hickory, ginkgo, beech and birch turn shades of yellow. As leaves return nutrients to the tree for winter storage, chlorophyll production dies back. The green fades, revealing yellow and orange pigmentation that was latent in the leaf.

Similarly, leaves of dogwood, sumac, white oak and sugar maples, not to mention poison ivy, turn red by a chemical process accelerated by cold.