By Guy Faulconbridge

MOSCOW (Reuters) - Russians prayed for Patriarch Alexiy II at services across the country on Saturday as the ruling body of the Russian Orthodox Church prepared to select an interim leader after his death.

Alexiy, who forged close ties with the Kremlin under former President Vladimir Putin and helped revive the Church after the collapse of the Soviet Union, died on Friday at his residence outside Moscow. He died of heart failure after a long illness.

At Orthodox church services across Russia's 11 time zones, people said prayers through the night for Alexiy, who helped heal an 80-year rift with a rival faction set up abroad by monarchists fleeing the atheist Bolsheviks.

A Holy Synod will meet on Saturday to elect an interim Patriarch, known as the Patriarchal Locum Tenens. A wider synod will then convene to elect a new leader within six months.

"A session of the Holy Synod of the Russian Orthodox Church will take place on December 6 to elect Patriarchal Locum Tenens who will chair the Memorial Commission," a spokesman for the Moscow Patriarchy said.

Alexiy will be laid in state on Saturday in the giant Christ the Saviour Cathedral in central Moscow, rebuilt during Alexiy's reign after its destruction under Stalin. His funeral will take place on Tuesday, the Patriarchy said.

Believers laid hundreds of red and white roses at the Patriarch's office in central Moscow, a Reuters reporter said. White roses were said to be Alexiy's favorite.

Alexiy, who criticized the Catholic Church for trying to steal converts, is credited by many Russians for helping to revive Orthodoxy and boost church attendance in the moral and spiritual vacuum created the collapse of the Soviet empire.

Despite Soviet-era suppression of believers -- and the destruction of hundreds of churches under Stalin -- Orthodoxy remains a key part of life for millions of Russians.

ALEXIY'S LEGACY

Alexiy also steered a careful path for the Orthodox Church, which was riddled with divisions, especially during the upheavals of the 1990s.

"Alexiy's main achievement was to keep the Church together in this period of growth and turmoil," Andrei Zolotov, an expert on the Russian Orthodox Church, said by telephone from the United States.

"The Patriarch steered a very careful centrist path in the development of the church when it was threatened with being literally being torn apart politically, theologically and in many other regards too," Zolotov said.

Putin and President Dmitry Medvedev, who both attended major Orthodox Ceremonies with Alexiy, praised the Patriarch's role in helping form Russian statehood and for uniting the nation.

Supporters said Alexiy harnessed close ties with the state for the benefit of the Church, restoring hundreds of almost derelict churches.

Opponents said he allowed the Church to become a minor partner of the Kremlin under Putin. Alexiy failed to shake off allegations he had links to the Soviet KGB. The Church has repeatedly denied that.

The next Patriarch has to be chosen within six months and observers said there is a group of about four main candidates who are being talked about as possible successors.

The Church's relations with the state and the Catholic Church are key issues. The following are key candidates:

* Metropolitan Kirill, who heads the Church's foreign relations department, is seen as a ambitious reformer who would seek to make the Church a more independent partner of the state. He is perceived to be open to cooperation with Catholics.

* Metropolitan Klement of Kaluga and Borovsk, who manages the Church's economic affairs, is seen as a loyal follower of the Patriarch who some insiders say is happier to see the Church as a servant of the state. He is seen as more conservative.

* Metropolitan Juvenali, who has been the ruling bishop of the Moscow region since 1977, is a survivor who sources say could be seen as a compromise figure.

* Metropolitan Filaret of Minsk, the capital of Belarus, is a charismatic bishop with flair who could be seen as a compromise figure between Kirill and Klement. He is seen as a modernizer.