THE BRINK of reform is a dangerous place. Just look at Tehran, where Abdullah Nouri, a prominent cleric who was once a deputy to reformist President Mohammed Khatemi and before that to Ayatollah Khomeini, has been on trial. Charged with apostasy and treason, Mr. Nouri has daily been denouncing the court's legitimacy, defending his right to speak and criticize, and naming taboo figures from the recent past--all in the hearing of an astounded Iranian and world press corps.

Not unlike Mr. Khatemi, Mr. Nouri has moved from his conservative clerical roots--far enough so that conservative forces impeached him from his government position several years ago. He later became editor of a daily newspaper, Khordad, which has carried the reformist banner in a high-hazard atmosphere of alternating press freedom and conservative crackdowns. Mr. Nouri was expected to be the top vote-getter of any reformist slate in upcoming parliamentary elections. Until, that is, the clerical court indicted him on 44 pages of charges--an evident effort to disqualify him from standing for office.

But the unfolding trial went past the expectations of the clerical court, which is controlled by the conservative mullahs struggling to contain the Khatemi reforms. Mr. Nouri has met the charges against him--that his newspaper insulted Islam, that he advocates a resumption of ties with the United States, that he supports Israel, that he advocates allowing clapping at concerts, an Islamic taboo--with strong avowals. He says that to discuss a topic freely is not to support it and that it is the clergy court, not he, that has "betrayed the revolution."

The clerical jury, whose role is advisory, has recommended conviction for Mr. Nouri, and the judge is expected to confirm that judgment. But the mullahs, perhaps fearing public backlash, have been unable to shut down coverage of the trial or to force Mr. Nouri to submit his defense in writing instead of orally. Mr. Nouri may pay a heavy price for his daring. But if we learned anything from the fall of dictatorships a decade ago, it's that there's no predicting events once controls on expression begin to loosen.