Brussels — ''You are the fruit of my life,'' Ayatollah Khomeini once told Hossein Ali Montazeri, who was his student. Now Ayatollah Montazeri is considered the likely heir to Khomeini's position as Iran's ''spiritual guide.'' Five years after the establishment of the Islamic Republic, the 61-year-old Montazeri is emerging as one of its most articulate leaders.
Residents of Qom, a holy city 90 miles south of Tehran, are used to seeing this grizzly-bearded professor of Islamic law every day on his way to the Elmieh Theological School. Montazeri frequently receives visitors from all over the country.
Montazeri's speeches tend to be more logical and straightforward than those of other revolutionary mullahs. He also tends to deal with concrete problems, while Khomeini confines himself more and more to religious issues.
''Punishing someone who is not guilty is worse than leaving a crime unpunished,'' Montazeri reminded a group of revolutionary judges recently. He was referring to the jailing and execution of innocent people.
A few weeks later he asked the Cabinet to pay more attention to Iran's raging inflation and deplored the fact that ''qualified people had been laid off after having been tested on futile questions.'' He was alluding to the tests of knowledge of the Koran organized by some government ministries and state-owned companies. This statement sharply opposed revolutionary theories that stress that a person's religious faith is more important than his manual and intellectual capacities.
A few weeks ago the Iraqis bombarded an Iranian border town. This was described by most Iranian leaders as ''a new crime of American imperialism.'' But Montazeri candidly pointed out that the missiles were made in the Soviet Union.
Nevertheless, top government officials would like to see him succeed Khomeini. Some opponents of the regime say Montazeri is a threat to Khomeini's power, but so far this charge has proved untrue. Montazeri fully supports the principle of having a religious guide for the nation. He backs all revolutionary institutions created since 1979. He shares Khomeini's strong anti-American views. And he believes Iraqi President Saddam Hussein should be overthrown, one of Iran's goals in the war with Iraq.
When Khomeini dies, Iran's religious assembly will choose a successor. If it cannot agree on one person, it will elect a council of three to five mullahs. If Montazeri is not chosen as the sole guide, he is at least certain to be named a member of the council.
Montazeri has long been closely linked with the fight to establish an Islamic republic in Iran. On June 5, 1963, the Shah ordered the Army to fire onto a crowd that had assembled near Tehran bazaar to protest the arrest of a little known ayatollah who had made an anti-imperial and anti-American speech.
That ayatollah was Khomeini. Montazeri, one of his active supporters, was jailed for a few months a few weeks later. Between 1963 and 1978, Montazeri had only brief periods of freedom, spending most of his time either in jail or in internal exile.
A few months before the Shah was overthrown in February 1979, the imperial authorities released Montazeri from jail. He immediately flew to France to renew his allegiance to Ayatollah Khomeini, who was in exile in a tiny village near Paris.
''Ayatollah Khomeini taught me everything,'' he told a group of journalists at the time.
When the imperial regime crumbled, both ayatollahs put their theories on the theocratic republic into practice. Khomeini became the spiritual guide. And Montazeri, although at first not given an influential position because of poor health, later presided over the constituent assembly that wrote the new constitution.
At that time Western observers considered Montazeri a low-key revolutionary leader. In his Friday prayer sermons he echoed Khomeini's ideas. He was known for his grandiloquent rhetoric on the export of the Islamic revolution. Opponents charged that he suffered from early senility. But those close to him relentlessly repeated that he needed rest and was only handicapped by minor memory problems because of ''the tortures he endured in the imperial jails.''
The somewhat extravagant behavior of his son also hurt his image. Muhammad Montazeri, a young clergyman in his 30s, paraded around Tehran with a highly visible armed escort. Nicknamed Hojatolislam Ringo by his opponents, the junior Montazeri allegedly carried handguns under his robe. Early in 1980 he was assassinated in Lebanon while on a trip with a contingent of Iranian Revolutionary Guards.
Rumors that the senior Montazeri was Khomeini's heir apparent first began to circulate in Tehran in the spring of 1980, a few weeks after Khomeini suffered a severe heart attack. Throughout the hostage crisis and the feud between President Abolhassan Bani-Sadr and the clergy, Montazeri kept a low profile.
In November 1982 the Iranian government started to prepare for the election of the religious assembly. At the same time Montazeri reappeared in newspaper headlines. Journalists referred to him as the ''grand ayatollah'' and emphasized the ''guidelines'' he issued to his visitors. Nowadays one cannot read an Iranian newspaper without seeing Montazeri's name.