MOSCOW — Russian Orthodox Patriarch Alexy II, who presided over a vast post-Soviet revival of faith but struggled against the influence of other churches, died Friday at age 79.

The Moscow Patriarchate said he died at his residence outside Moscow, but did not give a cause of death. Alexy had long suffered from a heart ailment.

Alexy became leader of the church in 1990, as the officially atheist Soviet Union was loosening its restrictions on religion. After the Soviet Union collapsed in 1991, the church's popularity surged. Church domes that had been stripped of their gold under the Soviets were regilded, churches that had been converted into warehouses or left to rot in neglect were painstakingly restored and hourslong services on major religious holidays were broadcast live on national television.

By the time of Alexy's death, the church's flock was estimated to include about two-thirds of Russia's 142 million people, making it the world's largest Orthodox church.

But Alexy often complained that Russia's new religious freedom put the church under severe pressure and he bitterly resented what he said were attempts by other Christian churches to poach adherents among people who he said should have belonged to the Orthodox church.

These complaints focused on the Roman Catholic Church, and Alexy refused to agree to a papal visit to Russia unless the proselytization issue was resolved.

Nonetheless, the Vatican praised his efforts to discuss the problems.

"His personal commitment to improving relations with the Catholic Church in spite of the difficulties and tensions which from time to time have emerged has never been in doubt," said Cardinal Walter Kasper, president of the Pontifical Council for Promoting Christian Unity.

Alexy lived long enough to see another major religious dispute resolved. In 2007, he signed a pact with Metropolitan Laurus, the leader of the breakaway Russian Orthodox Church Outside Russia, to bring the churches closer together. The U.S.-based Church Outside Russia had split off in 1927, after the Moscow church's leader declared loyalty to the Communist government.

Alexy successfully lobbied for the 1997 passage of a religion law that places restrictions on the activities of religions other than Orthodoxy, Islam, Judaism and Buddhism. Under his leadership, the church also vehemently opposed schismatic Orthodox churches in neighboring Ukraine, claiming the Ukrainian church should remain under Moscow's control.

A top representative of Russia's Muslims praised Alexy's efforts to restore religion's prominence in post-Soviet Russia.

"All the activities of this man were devoted to unifying our country, developing state-religion relations and the dialogue of Russia's traditional faiths," said Albir Krangov, a deputy chairman of the Muslim Central Spiritual Administration, according to the RIA-Novosti news agency.

In a demonstration of the close relations between church and state, President Dmitry Medvedev canceled plans to travel from India to Italy, so he can return for the funeral, whose date has not been announced. "He was a great citizen of Russia. A man in whose destiny the whole difficult experience of our country's changes in the 20th century are reflected," Medvedev said.

The patriarch was born Alexei Mikhailovich Ridiger on Feb. 23, 1929, in Tallinn, Estonia. The son of a priest, Alexy often accompanied his parents on pilgrimages to churches and monasteries, and he helped his father minister to prisoners in Nazi concentration camps in Estonia. It was during those visits that Alexy decided to pursue a religious life.

Under Soviet rule, this was not an easy choice. Lenin and Stalin suppressed religion and thousands of churches were destroyed or converted to other uses, such as museums devoted to atheism or, in some cases, stables. Many priests and parishioners were persecuted for their beliefs.

The persecution eased somewhat during World War II, when Stalin discovered that the church could be used as a propaganda tool in the fight against the Nazis. But the Soviet authorities never fully loosened their grip, penetrating the church at the highest levels.

Alexy was ordained in 1950, progressed through the Orthodox hierarchy, and was consecrated Bishop of Tallinn and Estonia in 1961.

The British-based Keston Institute, which monitors religious freedom in former Communist countries, has cited research suggesting that Alexy's career may have been aided by assistance he gave the KGB while a young priest in Tallinn. Orthodox Church officials vehemently denied the allegations.