THAT chorus of Democratic bleats about the free television time given President Reagan for a speech Wednesday suggests that this was an unprecedented partisan abuse of executive power. After all, wasn't that a "political" speech, thinly disguised as a presidential address to qualify as "news"? And if so, why didn't all the networks treat it either as a paid political broadcast or as a program that should automatically include opposing views of equal duration?

Mr. Reagan may be the most skilled president ever when it comes to using television, but he certainly is not the first to seize the advantage that comes with the job. Every chief executive since the invention of radio has figured out that, with little or no indication of what he wants to talk about, a president can commandeer free air time at once, at almost any hour he chooses. What's a network to do?

The dilemma for broadcasters (including, we note, The Washington Post Company's television stations) is that this practice does have a built-in imbalance: the networks' willingness or commitment to cover "news" can be exploited to deliver one side of a public issue with no comparable format or formula for differing viewpoints. So it was that the networks each responded differently this time, as did some of their affiliated stations.

NBC carried the speech, as well as a short Democratic reply presented by Sen. Don Riegle of Michigan. CBS broadcast the speech, but not the reply of Mr. Riegle, who is a candidate for reelection this year -- which raised a question as to whether "equal time" regulations applied for his opponents. ABC chose not to carry a live broadcast. Affiliates made their own decisions; some broadcast the speech or speeches on a delayed basis.

This variety of responses makes sense. Equal time provisions can be unfair, in that they cause broadcasters to shy from any offers of free time that could require extraordinary amounts of "equal time" offers to entire fields of candidates or political parties.

There is always "politics" in a presidential speech; the argument is over exactly how much. A president, by virtue of his office, is likely to win better ratings than any appointed opponents who may take to the air to disagree with him. While the networks prefer some discretion in what they choose to do with their time, the listener already enjoys that option -- through a flick of the dial.