RED CLOUD, Neb.: Junction of Rtes. 136 and 281 in south-central Nebraska, near the Kansas border.
* Willa Cather Pioneer Memorial Museum and Archives, 338 N. Webster St. (402-746-3285). Open April 1-Nov. 15, Monday-Saturday 8-5; Sunday 1-5; other times, Monday-Friday 1-5. Starting point for tours of Cather literary landmarks; offers guided town tours, and map for an independent walking tour and for a self-guided driving tour of "Catherland," 50 miles in Webster County.
* Willa Cather's childhood home, corner of Cedar and Third streets, may be toured separately.
* Willa Cather Memorial Prairie, 610 acres, 5 miles south of Red Cloud on Rte. 281. SAUK CENTRE, Minn.: Off I-94 in central part of the state.
* Sinclair Lewis Interpretive Center, junction of I-94 & US 71. Open Memorial Day-Labor Day 10-6; other times, 10-4.
* Sinclair Lewis Boyhood Home, 812 Sinclair Lewis Ave., off Main Street (612-352-6892). Open Memorial Day-Sept. 1, daily 10-6.
Palmer House Hotel and Restaurant, corner of Sinclair Lewis Avenue & Main Street (612-352-3431). CLYDE, Ohio: On Rte. 20, just south of Ohio Turnpike between Cleveland and Toledo.
* Clyde Museum, in basement of Clyde Public Library, 222 W. Buckeye St.
* Sherwood Anderson Boyhood Home, 129 Spring Ave., not open to public. HANNIBAL, Mo.: Rte. 61, 100 miles north of St. Louis.
* Historic Hill Street and Main Street district:
* Mark Twain Boyhood Home & Museum, 208 Hill St. Open Memorial Day-Labor Day, daily 8-6; other times (except holidays), daily 10-5.
* Becky Thatcher House, Judge Clemens' law office, Grant Drug Store, in the same block, same schedule as Twain's home.
* Steamboat Landing. Sternwheeler "Mark Twain" one-hour excursions on the Mississippi; at the foot of Center Street. Embarks Memorial Day-Labor Day, daily 11 a.m., 1:30, 3, 4:30 and 7 p.m.
* Twainland Express, one-hour tram tours, narrated; at Hill & Third streets. Open late May to September, daily 10-5.
* Clemens Amphitheater, outdoor drama "Reflections of Mark Twain," four miles south on Rte. 61. Open May 31-Sept. 3, evening performances, except Sunday (May and October, Friday and Saturday only).
* Mark Twain Cave, 55-minute tour, two miles south on Rte. 79. Open Memorial Day-Labor Day, 8 to 8 daily; other times, 9 to dusk.
* Also in Hannibal: Riverview Park, Cardiff Hill, Lover's Leap, Mark Twain Memorial Lighthouse, Tom Sawyer Dioramas, Rockcliffe Mansion, Garth Woodside Mansion, Molly Brown House, etc. FLORIDA, Mo.: State Road 107 via US 24, 30 miles southwest of Hannibal.
* Mark Twain Birthplace Memorial Shrine in Mark Twain State Park. Open Memorial Day-Labor Day, Monday-Saturday 10-5; Sunday 12-6; other times 12-5. Useful literary guidebooks include "No Castles on Main Street" by Stephanie Kraft, Rand McNally, 1979; the "Midwest and Great Plains States" section of "The Oxford Illustrated Literary Guide to the United States," eds. Eugene Ehrlich and Gorton Carruth, Oxford University Press, 1982; and Rita Stein's "A Literary Tour Guide to the United States: West and Midwest," William Morrow, 1979. Biographies, such as Mark Schorer's "Sinclair Lewis: An American Life" and Dixon Wecter's "Sam Clemen's of Hannibal," would be helpful to the literary sightseer. But it would probably be best to reread the books themselves--"Tom Sawyer" and "My Antonia" and "Main Street" and "Winesburg, Ohio"--while visiting the towns they recreate.