MOSCOW — The Russian Orthodox Church, in a gathering Tuesday at Moscow’s grandest cathedral, elected an outspoken new leader to succeed Patriarch Aleksy II, who died on Dec. 5 after guiding the world’s largest Orthodox church through nearly two decades of reconstruction and revival in the post-Soviet era.

Metropolitan Kirill of Smolensk and Kaliningrad, an articulate critic of declining moral values in the modern world who has been actively involved in the ecumenical movement and called for the Russian Orthodox Church to step up its outreach in secular society, was elected overwhelmingly. He has served as locum tenens, or interim patriarch, since Aleksy’s death.

At a meeting Sunday of the church’s hierarchs, the Archbishops’ Council, Kirill spoke in tough terms about threats to church unity, especially in Ukraine. The Orthodox church in Ukraine has broken into rival groups since the collapse of the Soviet Union. The largest is still loyal to Moscow and accounts for more than one-third of the entire Russian Orthodox Church, but calls are growing for its independence, or autocephaly in church terms.

More than 700 delegates representing the hierarchy, clergy, monastics and laity of the church convened to make their choice at Christ the Savior Cathedral, within view of the Kremlin. The original cathedral, which was blown up at Stalin’s orders in 1931 and rebuilt in the 1990s, has become a symbol of the church’s revival in Russia.

The delegates were choosing from a short-list of three candidates chosen by the Archbishops’ Council on Sunday. One of the candidates, Metropolitan Filaret of Minsk, who has been credited with reviving the Orthodox church in Belarus and treading a careful path in relations with the Belarussian president, Aleksandr Lukashenko, withdrew his name from consideration.

On Tuesday, after the hierarchs in blue and purple robes walked in procession into the center of the cathedral, the Local Council opened with prayers invoking the Holy Spirit.

The race for the patriarchal throne played out almost like a contemporary political campaign, with passionate debates on blogs and Web sites about the course the church and the new patriarch should take.

Outside the cathedral, activists of the Orthodox corps of Nashi, a pro-Kremlin youth movement, held banners in support of church unity and expressing confidence that the right choice would be made.

“The Holy Spirit Will Point Out The Worthy One,” read one of their banners.

Kirill, 62, was born in Leningrad into a clergy family. Both his father and grandfather were priests and served time in Soviet prison camps.