WITHOUT EVEN waiting for the next telethon fund-raiser, Walter H. Annenberg has sent a little something along to keep public television alive and provocative: a tidy $150 million donation to the Corporation for Public Broadcasting to support the first big national effort in this country to produce college-level courses on the home screens as well as on radio. Coming as it does at a time when the word from another sponsor -- the government -- is about a possible 25 percent cut in the corporation's budget next year, the gift is all the more welcome.

The idea of this college-of-the-air project is to use the latest advances in broadcasting to produce high-quality programs that might be offered by colleges at lower fees than those charged for traditional courses. Initially, Mr. Annenberg said he thought the courses would be aimed primarily at young people 18 to 21; but members of a task force that worked out details of the project have convinced him that the programs are likely to attract mostly older students.

Whatever the eventual makeup of the "student body," the project is immensely intriguing. No, there's nothing like the good old in-person presence of a great mind to stimulate the intellect; and yes, memories of the old kinescoped, pompous-man-with-blackboard lectures hardly stimulate a lobby for copies of those musty air-looms. But to write off modern broadcasting methods -- including the still unfathomed possibilities of two-way cable systems -- as unworthy of consideration for true higher education is foolish.

The very strength of public broadcasting has been its ability to expore new concepts -- incuding public use of and access to the airwaves for cultural and other special enrichment. The very weakness has been the limitation on money available.Now, Mr. Annenberg's unprecedented generosity opens up new possibilities for creative contributions. Anybody ready with a matching gift?