WORTH NOTING ON TV

* WEDNESDAY

The New Explorers With Bill Kurtis (PBS, 8-9 p.m.): Machu Picchu, the fabled lost city of the ancient Inca Empire, was discovered by an archaeologist in 1911, but questions about the city's purpose and short history have persisted. This program, entitled ''The Mystery of Machu Picchu,'' travels to Peru with several ''new explorers,'' including amateur archaeologist Jim Westerman, who proposes a debatable solution to the puzzle.

American Masters (PBS, 9-10:30 p.m.): ''By photographing what I was afraid of or what I was interested in,'' says groundbreaking photographer Richard Avedon, ''I explored and learned.... It got out of my system and onto the page.'' This in-depth self-portrait of the fashion and portrait photographer celebrates the 10th anniversary of ''American Masters,'' a series profiling important figures in American culture. The special, entitled ''Richard Avedon: Darkness and Light,'' showcases Avedon's style and many of his striking - and sometimes controversial - shots, including the majestic ''Dovima and the Elephants'' and a jarring portrait of author Isak Dinesen.

* THURSDAY

Smithsonian Fantastic Journey (CBS, 8-9 p.m.): First of two specials celebrating the 150th anniversary of the Smithsonian Institution. ''Smithsonian Fantastic Journey'' takes viewers around the world to current Smithsonian research projects, where more than 8,000 scientists and scholars explore such topics as elephant behavior, volcano activity, and marine life on the ocean floor.

In another segment, Kermit the Frog reports on the Smithsonian's two-year, 12-city tour of the US to exhibit 300 national treasures. The tour involves 500 Smithsonian employees, 30 full-time security personnel, 25 trucks traveling 500,000 miles, 1,000 graphic images, and 100,000 square feet of exhibit space.

Please check local listings for these programs.