And that’s the way it is at Discovery Communications.Legendary newsman Walter Cronkite has signed a three-year contract with the parent of the Discovery Channel and the Learning Channel, under which he will appear as an on-air personality and contribute to the production of several specials and series on its two networks. Key element of the agreement is that the 76-year-old CBS News veteran will not work for any other cable TV network for the duration of the contract. Cronkite hosted “Dinosaur!,” a four-part series on the animals that once ruled the earth, on the Arts & Entertainment Network in 1991, and “How to Prevent a Heart Attack” for HBO in June. As part of the agreement, Cronkite also will serve as an editorial adviser to the news and documentary portion of its new “Your Choice” TV remote control device. Bethesda-based Discovery announced last week it has a patent pending for a TV remote control permitting users to easily peruse hundreds of channels. The device will come with traditional numbers as well as 11 buttons with symbols representing programming genres. Cronkite will advise Discovery on which news and documentary programs it should highlight on “Your Choice.” It is also possible he could appear on-air, introducing news and docu topics on the system. Cronkite stepped down from his position as anchor and managing editor of the “CBS Evening News” in 1981. The man hailed as “the most trusted man in America” during his 19-year tenure at the CBS News helm is currently a consultant to CBS Inc. He was a member of the board until last year. The Discovery deal does not interfere with his activities at CBS. At Discovery, Cronkite will anchor and serve as exec producer on quarterly specials addressing national and international topics entitled “Walter Cronkite’s World.” There is no firm air date yet for the first special, although it will be sometime in first quarter ’93. Cronkite also will serve as exec editor of “Understanding,” a quarterly series of specials that will try to explain complex scientific topics to laymen, on Discovery. He will hold the same title for “Great Books,” specials on influential works of literature, such as Charles Darwin’s “On the Origin of Species,” on the Learning Channel. The shows are co-produced with Discovery and Cronkite/Ward, a new company Cronkite has formed with longtime CBS associate Jonathan Ward. The partners will participate in the profits from the sales of these programs to other markets, including homevideo. Cronkite has had a long relationship with Discovery. When president/CEO John Hendricks was trying to put together the financing to launch Discovery in 1982, Cronkite wrote a letter of support, which helped spur investor interest. Cronkite was anchor and exec producer of “The Presidential Candidates: Address to the Nation,” which aired on Discovery in March.