Fall brings out the walker, hiker, boater and natural scientist in almost anybody. Here's a list of activities that focus on foliage and get you out exploring in the autumn air. ON FOOT

FALL LEAVES, MUSHROOMS & SPIDERS -- Saturday, 10, at Watkins Nature Center, 301 Watkins Park Drive, Largo. A nature hike. Free. 249- 6202.

AUTUMN HIKE -- Saturday, 10, meet at Rock Creek Park Nature Center, 5200 Glover Road NW. A park ranger leads a 11/2-hour hike to observe the colors of fall. Wear sturdy shoes. Free. 426-6829.

TREE STUMPERS HIKE -- Saturday, 2 to 3:30, Potomac Overlook Regional Park, end of Marcey Road, Arlington. Hikers will learn to identify local deciduous and coniferous trees. Free. 528-5406.

PRESSED FLORA ART -- This Saturday and next, October 27, 9:30 to 11:30, Woodend, Audubon Society Headquarters, 8940 Jones Mill Road, Chevy Chase. Collect autumn leaves and flowers in the first Saturday session and design a collage in the second session. Aimed at adults and children over 10. Audubon Society members $12, non-members $16. 652- 5964.

COLORS OFF-THE-TRAIL HIKE -- October 20, 10 to 11:30, meet at Ellanor C. Lawrence Park, Centreville, for a hike with naturalist Kate Noonan along Big Rocky Run. Free. 631-0013.

CHANGING FALL COLORS -- October 21, 2 to 3, Hidden Oaks Nature Center, 4030 Hummer Road, Annandale. A family trail walk with a naturalist to learn about the chemical changes that create autumn colors. Free, canceled if rain. 941-1065.

TRACKS TRAIL -- sponsors fall color outing October 21 at 2. Free. Call 451-9588.

BEGINNING TREE IDENTIFICATION -- October 27, 1 to 4, Audubon Society field trip to Rock Creek Park, leaving from Woodend, 8940 Jones Mill Road, Chevy Chase. An introductory foray to learn tree recognition techniques. Audubon Society members $12, non-members $17. 652- 5964.

POTOMAC COLORS -- October 28, 10 to 11:30, Riverbend Park, Great Falls, Virginia. A hike with a naturalist along the Potomac, to learn how leaves change color, how to recognize trees and how to spot other seasonal signs. Free, canceled if rain. 759-3211. ON WATER

AUTUMN CANOE TRIPS -- This Sunday and October 28 & November 4, 8 a.m., Pohick Bay Regional Park, Lorton exit off I-95. A three-to-four hour interpretive canoe trip through the marshes near Pohick Bay. For paddlers 16 and over, no experience necessary; all equiipment provided. Bring a lunch and beverage. $10 per person, reservations required. 352- 5900.

FALL COLORS CRUISE -- October 21, Fountainhead Regional Park, off Route 123 south of Fairfax. A 11/2-hour cruise along the Occoquan River in a pontoon boat to see and learn about autumn changes. Advance reservations required. Adults $3, children 11 and under $1.50. 528-5406.

FALL COLORS OUTING -- October 21. A rafting tip with American Rivers Conservation Council on the New River in West Virginia. For newsletter and trip list, call 547-6900. ON A BICYCLE

FANTASTIC FOLIAGE PEDALS -- Saturday and Sunday, through the Blue Ridge foothills in Clarke County, Virginia, with American Youth Hostels. Two nights (dorm style) and most meals included for $70. Potomac Area Council, 783-4943.