MYRON FARBER, a reporter for The New York Times, went to jail Friday, and a fine of $5,000 a day against The Times went into effect. Mr. Farber will stay in jail, and the fine payment will grow, either until a murder trial ends or unitl The Times decides to hand over to the judge some 4,000 pages of material. Much of that material was acquired with assurances that its sources would not be revealed. This predicament exists because Mr. Farber and The Times are trying to establish that there is a constitutional privilege permitting reporters and newspapers to refuse to disclose their fonfidential sources. They may yet be successful in their effort. No court has yet ruled in their case that this privilege does not exist. But the price they are paying to get the question resolved is heavy.

More than a dozen judges have been involved in this case, and most have ruled that The Times is forcing this basic question prematurely. Only after the 4,000 pages have been turned over to the judge, their argument goes, will the courts decide whether The Times and Mr. Farber have a privilege not to disclose the information.

In adopting this course, the judges appear to be following the doctrine of the Supreme Court's decision in the Nixon tapes case. There are two striking resemblances between the cases.Richard Nixon, like The Times and its reporter, was confronted with a subpoena requiring the production of material he regarded a confidential. And Mr. Nixon, like The Times, asserted a constitutional privilege against being compelled to disclose such information.

From those two similarities, it is easy (and tempting for a judge) to take the next steps. Because the Supreme Court said Mr. Nixon's privilege must yield, in an appropriate situation, to the demands of fundamental fairness in a criminal case, so (it can be concluded) must the press privilege similarly yield. And because the court told Mr. Nixon to give the tapes to a trial judge who would then decide whether the privilege applied to the conversations on them, so (it can again be concluded) must the Times give its material to a trial judge for a similar inspection. The comparison even goes one step further. In the Nixon case, the courts enforced the request of a prosecutor for material that might be useful in convicting someone of a crime; in the Times case, the request is that of a defense lawyer seeking material that might be useful in winning an acquittal for someone accused of crime.

There are differences, of course. Mr. Nixon was asserting a privilege that springs from presidential power. The Times is asserting one that grows from the First Amendment. The president has a formal role in the administration of justice; the press does not. The material sought from Mr. Nixon involved his own allegedly illegal acts; that sought from The Times involves no illegal acts on its part. Whether those or other differences are sufficient to distinguish the two cases is an open question. That will be decided when the Supreme Court is faced with a pure case involving the reporter's privilege.

The problem with the Times case is that it is being treated, by the courts and the press, as if it were just such a pure case when, in fact, it is not. Two critical differences, largely brushed aside by the judges, change the balance. The first is that The Times is being required to surrender its material before it gets a ruling on its basic claim. Mr. Nixon was told to hand over the tapes only after the Supreme Court spoke and after it provided the trial judge with instructions on the limits of that privilege. No such limits have yet been established on the press privilege.

The second difference - one that is even more important in its long-term effect on the press - is the scope of the order The Times is being told to obey. Mr. Nixon was required to surrender only specific tapes that contained conversations with specific persons on specific subjects. The Times and Mr. Farber are being told to surrender everything in their possession - notes, pictures, memos and so on - concerning more than 100 persons. That sweeping order appears to us to be in the nature of a fishing expedition in which the defense lawyer hopes to catch something useful. That makes it different from the order in the Nixon case, where the prosecutor knew precisely what he wanted. Indeed, a federal court here refused five years ago to enforce a similar sweeping subpoena for all of this newspaper's Watergate materials on the ground that it violated the Fourth Amendment, which prohibits unreasonable search and seizure. This aspect of The Times case has almost dropped out of sight because of the intense focus of the judges, lawyers and the press on the First Amendment privilege question.

It would be crippling to investigative journalism for the courts to rule eventually against the reporter's privilege in a situation precisely paralleing the Nixon case.But it would be disastrous to journalism in general and to the individual rights of all citizens to have the courts uphold a subpoena as broad as the one issued to The Times. Such a holding would mean that any defense lawyer in any case could fish in almost anyone's private files without specifying what he expected to find there.

Thus, The Times and Mr. Farber are caught in a ghastly trap. They can't get their fundamental argument heard until they disclose the very material they are seeking to protect. They can't disclose the material without violating their promises to dozens of sources and, at the same time, complying with an order that is so outrageously and dangerously broad as to create a horrendous precedent. The course they have chosen is painful and costly, but it is also - if that is any consolation to a man in jail - honorable.