EMBARRASSED BY a story in The Washington Times, the House ethics committee has retaliated by serving a subpoena on the offending reporter, Thomas D. Brandt. It is an attack that does no credit to either the committee's judgment or its understanding of the Constitution.

Mr. Brandt had obtained a draft of the committee's report on the interesting subject of Rep. Geraldine Ferraro's financial reports. When The Washington Times put his story on its front page, that forced the committee to release the report a good deal sooner than it evidently had intended to do. All of which seems to have caused much rage, anxiety and aggravated heartburn in the committee's offices. But it violated no security classification, or any other law.

On the contrary, the committee's action was a wholly proper subject of public discussion and should have been made public as soon as the report was written and the committee's vote was taken. The Ferraro case sets an important precedent under the rules governing the reporting of political money. No doubt the committee and its chairman, Louis Stokes, are sore. But Mr. Brandt and The Washington Times served their readers well -- and the public interest.

What does the ethics committee have in mind with this subpoena? You can't get an answer by asking them. The chairman and the committee's staff refuse any comment, saying only that their rules forbid any explanation. They won't even acknowledge that a subpoena was issued. What does Mr. Stokes think he's running, a grand jury?

There's an unpleasant suggestion of deliberate harassment and intimidation here. Fortunately, neither Mr. Brandt nor The Times seems to be impressed by it. The committee ordered Mr. Brandt to appear Friday with various notes and so forth related to his story. He and The Times have refused, arguing that they cannot disclose their sources without eroding the protection that the First Amendment provides not only to reporters but to all citizens.

A congressional committee has a right to keep its papers secret -- if it can. If it can't, it is not entitled to reporters' help. It is most emphatically not entitled, in the absence of any crime, to threaten reporters and to coerce their testimony. Who says so? The First Amendment. But like any law, it will retain its vigor only so long as citizens use it and demand that it be honored.