Walter Cronkite retired? He's all over the tube

The reports of Walter Cronkite's retirement are highly exaggerated. Fans of ''Uncle Walter'' may see him on the air as the host of two programs in the next few days, but the fact is that his alleged retirement is not over at all. According to Mr. Cronkite himself, ''It hasn't even begun.''

CBS News Special: The Great Nuclear Arms Debate (CBS, Saturday, 9:30-11 p.m.)m and I, Leonardo: A Journey of the Mind (CBS, Tuesday, 8-9 p.m.)m both feature Cronkite as moderator/host.

''I'm under an exclusive contract with CBS as a special correspondent and my retirement won't begin for at least five more years,'' he explained to me the other day. ''Next on my schedule is a special about George Orwell's '1984.' I've been working on that all winter, shooting all around the world. It's an exciting show, and now it looks as if it will be aired on CBS sometime in June. The only thing I retired from was the Evening News.''

How does ye olde avuncular anchor feel about the job being done now by his replacement, Dan Rather?

''He's doing a splendid job. But I have a little question in my mind as to the direction of the news process on the broadcast. It's a little too featurized. Not hitting hard enough in some aspects. But obviously it's successful as it is. . . .''

Isn't the trend toward headlines and feature news true of all the network evening news shows?

''Yes. And the only thing that may stop the pattern is more time. More time has been needed all along but I don't see evidence that any of the networks will be going to a full hour in the early evening as they should. It seems to be impossible because the station affiliates don't want it.'' He is hoping that the expanded ''MacNeil-Lehrer Report'' on PBS and the one-hour Ted Koppel ''Nightline'' on ABC will fill in some of the news gaps. 'I, Leonardo'

Cronkite is a man of many excitements, and he does not find it difficult to be enthusiastically involved in several shows simultaneously. His Tuesday show, ''I, Leonardo'' is a kind of joyous da Vinci sampler. It is a dramatized and beautifully illustrated catalog of the thoughts, theories, experiments, and works of art of that Renaissance genius, whose life was spent in a search for learning and knowledge.

Mankind, to Leonardo, is a microcosm of the universe itself. ''Everything comes from everything; everything is made from everything; everything can be turned into everything'' he wrote in his notebooks.

''I Leonardo: A Journey of the Mind'' is really a special kind of special for network programmers. Chock-full of a series of shocks of recognition, it could be one of the year's most rewarding specials for many viewers.

Leonardo is portrayed by Frank Langella, Richard Burton narrates, and Cronkite takes viewers on a guided tour of the Smithsonian Institution, urging better scientific and technical education for tomorrow's youth. IBM, which sponsors the show, presents Mr. Cronkite's public service messages in lieu of commercials.

''The message of better scientific education is an important one, and IBM is to be congratulated not only for airing the show but also for giving up their own commercials,'' he said. ''Nobody has asked me to do more of that sort of thing, but I certainly wouldn't turn my back on it. I believe we owe it to the next generation to educate it for its own scientific future.'' 'The Great Nuclear Arms Debate'

Mr. Cronkite also hopes that his Saturday transatlantic debate on the deployment of new US nuclear missiles in Europe will be only the first of similar debates.

The formal debate, which will actually be taped today (Friday), will include former Secretary of State Henry Kissinger, British Defense Minister Michael Heseltine, former chief US arms negotiator Paul C. Warnke, and German opposition leader Egon Bahr. They will discuss the pros and cons of ''Resolved: The United States should proceed with its scheduled deployment of new nuclear missiles in Europe.'' Cronkite will moderate from New York; the participants will be linked by satellite from three other countries.

''This was one of the projects I conceived under my new contract, and they bought it,'' he explained. ''There has been so much political pressure from other countries as well as pressure here at home making the headlines. I feel it is quintessential that the American people have adequate background information on what it is all about.

''TV news has been criticized for not preparing people for crisis situations. It has been said that we don't let the public know until trouble is already brewing, until the rocks are thrown. We ought to try to avoid that. In a democracy, people should be familiar with all arguments. I hope we can establish a continuing dialogue of information as well as opinion in this big transatlantic format.

''Almost any of the major issues of our time would be grist for this kind of mill. Wouldn't it be marvelous if we could have at least four debate specials a year on major issues? I think it would be important and would attract large audiences as well.''

What would Cronkite like the debate to accomplish? What would he consider a successful outcome for the program?

''If it simply opens up the dialogue and therefore the eyes and ears of the American people to this critical issue to the point where they fully understand the arguments pro and con. That would enable them to make up their minds as to the American direction in a manner which reflects that knowledge so well that both our friends and enemies overseas would at least respect us for making an informed decision on an issue which will have a major impact on all civilization on earth.'' On and About the Air

* Action for Children's Television (ACT) has filed a complaint with the FTC against General Mills Inc. for ''promoting an unfair and deceptive game of chance to children.'' According to ACT, the company is advertising six presweetened cereals in Saturday morning TV commercials that urge children to participate in ''Watch 'n Play,'' a game of chance in which children save cards from cereal boxes and match them with cards shown during the commercials. The prize is a Sony Watchman television.

ACT considers this campaign unfair and deceptive because it tries to convince them that if they play a game of chance they will win the prize. Nowhere in the commercial are the odds against winning stated.

* Are you absolutely certain that signed Andy Warhol poster you were thinking of buying was actually signed by the master himself?

A growing number of art forgeries have caused museums and galleries throughout the nation to hire art fraud detectives in the form of specialized chemists to utilize new technology to deter the forgers. Discover, the syndicated science show airing in the last week of April (check local listings)m, delves into that phenomenon as well as other current science developments.

* A program designed to increase the ability of seventh- and eighth-graders to communicate effectively will be available from the Agency for Instructional Television this September for use in schools throughout the country. The new classroom video series in language arts shows the youngsters how communications skills relate to their own lives. Viewers will see young people and adults solving common communications problems and using language arts skills successfully in real-life situations.

Already more than 120 noncommercial television stations in the US and Canada have indicated that they will broadcast the series during the coming school year. If your local school systems are not aware of the oppportunity to use the series in the classroom, it's up to parents to inform them.