* Church said there was clear winner in election

* About 40 percent of Congolese are Catholics

* Poll result expected to be delayed past Sunday

* U.N. rights body warns against violence (Adds U.S. deploying small military force to Gabon)

By Giulia Paravicini

KINSHASA, Jan 4 (Reuters) - Democratic Republic of Congo's electoral commission accused the country's Catholic Church on Friday of "preparing an insurrection" by saying it knows the winner of last Sunday's presidential election.

The commission is scheduled to release provisional results on Sunday but has said there could be delays because of the slow arrival of tally sheets.

Donatien Nshole, the secretary-general of the Church's bishops' conference, known as CENCO, said on Thursday its vote tallies showed a clear victor in the Dec. 30 election, a pronouncement widely seen as a warning to authorities against rigging the vote.

"The announcement of voting trends by Priest Nshole is likely to brainwash the population while preparing an insurrection that CENCO alone will be responsible for," commission president Corneille Nangaa wrote in a letter to CENCO president Marcel Utembi, seen by Reuters.

Nangaa said CENCO's declaration violated electoral law and a code of conduct signed by poll monitors that gives the electoral commission, CENI, alone the authority to announce results.

The Catholic Church is one of Congo's most powerful institutions, representing about 40 percent of its 80 million people.

The ruling coalition of President Joseph Kabila, which is backing his hand-picked successor Emmanuel Ramazani Shadary, also took aim at CENCO on Thursday.

The coalition "deplores ... the partisan, irresponsible and anarchic attitude of CENCO," said Barnabe Kikaya Bin Karubi, an adviser to Kabila and spokesman for Shadary.

The U.N. Security Council was briefed behind closed doors on the latest developments on Friday at the request of France. French U.N. Ambassador Francois Delattre said the 15-member body would continue to monitor the electoral process in Congo.

"The consolidation of the results must continue with transparency," Delattre told reporters. "We call on all actors for calm and restraint."

Observers and the opposition say the election was marred by serious irregularities. The opposition, represented by its two main candidates Martin Fayulu and Felix Tshisekedi, and Shadary's camp have all claimed they are on course to win, without posting specific figures.

Kikaya told Reuters Kabila had met Catholic bishops on Friday but provided no details.

The government says the election was fair and went smoothly.