Dramatic confrontations in Iran between hard-liners and reformers, suggesting that the Islamic Republic may be tottering, recall the lesson history taught Mikhail Gorbachev: A political system rooted in lies and repression cannot long survive the telling of truth that comes with free speech.

A few brave Iranians have chosen to act as though the freedom of expression preached by Iran's reformist president, Mohammad Khatami, actually prevails in the Islamic Republic. One stunning example is Dr. Hashem Aghajari, a university history lecturer and wounded veteran of the Iran-Iraq war, who was sentenced to death last month by the hard-line judiciary for a speech in which he called for ''Islamic humanism'' and ''Islamic protestantism.'' Aghajari castigated the ruling clergy for wanting ''to exercise total power'' and called for ''inalienable rights'' for everyone. He was convicted of blaspheming the Prophet Mohammed, insulting the Shiite imams of Iran, and insulting the state's ruling religious authorities.

Aghajari's death sentence set off a series of mass demonstrations that the hard-liners are trying to suppress with threats and attacks from vigilante groups loyal to the ultras. A leader of the vigilantes warned last week of a ''revolutionary jihad'' on elected reformists whom he called ''unfaithful lawmakers who have penetrated into the Parliament.'' From the other side, the reformist speaker of Parliament - who is also the brother of President Khatami - warned last Wednesday that the hard-liners' repressive response could create a ''situation that no one would be able to control.''

Only a clairvoyant could know if the current scenes of political conflict spilling into the streets foreshadow another Iranian revolution, this one against the clerical dictatorship. At present, the mullahs in power certainly do not seem to have lost the will to rule. Unlike the Soviet ruling class behind Gorbachev, the Iranian hard-liners have shown no reluctance to bring on a bloodbath if that is the price for retaining their political power and their control over gigantic economic conglomerates disguised as religious foundations.

Nevertheless, the Bush administration ought to assume that Iran may have entered a prerevolutionary period. In such a situation, the best US policy is to maintain a shrewd silence. Again and again, the hard-liners try to play the patriotic card by alleging that Iranian reformers are in thrall to the Great Satan. Indeed, four Iranian pollsters are now on trial on charges of espionage for publishing poll results indicating that 74.7 percent of Iranians want dialogue with the United States and nearly 50 percent approve of US policy toward Iran. Bush should say nothing that could be used to validate the accusations hard-liners level at Iran's reformists. Too many disasters in Iran over the past half-century were caused by US meddling.