Nobody ever accused Carl Sagan, the oracular host of ''Cosmos,'' of being Mr. Modesty. But compared with author Alvin Toffler, the portentous narrator of The Third Wave (PBS, Wednesday, May 23, 9-10:30 p.m.), Sagan would come across as being aloof as Greta Garbo.
''The third gigantic wave of change is being unleashed across the planet,'' Toffler thunders to the accompaniment of ominously foreboding music. And then he proceeds to outline a whole series of mini-revelations, previously revealed to the public in his 1980 best seller. Interesting, uncomplicated, if not world-shattering stuff.
First, it seems, there was the creation of an agricultural society. Then, the second wave was the Industrial Revolution, which appears to have run its course. Now, according to master prognosticator Toffler, we are entering the third wave as a new civilization replaces the old one, as our society ''discovers new ways of living and working together.''
According to Toffler, Silicon Valley in northern California may well be the Mesopotamian ''fertile crescent'' of tomorrow's civilization. The typical worker of tomorrow will probably be functioning most of the week from his ''electronic cottage'' - his home/office. And he will be tri-literate - in print, broadcast media, and computer.
''We will become the high-tech first wave,'' Toffler intones, then proclaims us ''the children of the third wave of history,'' getting his wavelengths just a bit mixed up.
The TV version of ''The Third Wave,'' written by Toffler himself and presented on PBS by KCET, Los Angeles, was two years and $2 million in the making. It is the result of global cooperation among Canadian, Japanese, and American production companies and involved 75 locations around the world. In Japan it was presented as a series of specials followed by interviews with Toffler and was voted the best NHK (Nippon Hoso Kyokai) program of 1983.
I must report, however, that ''The Third Wave'' on PBS comes rolling ashore in America as a hokey mix of the obvious, the obscure, the ridiculous, and the simplistic. Its pseudo-mystic prophecies are constantly overpowered by a melodramatic and mellifluous spray of electronic trickery and overproduction. Maybe you just have to read the book.