SANTIAGO, Chile (AP) _ Opposition leaders and Roman Catholic church officials said Monday they fear violence by pro-government provocateurs during this week's referendum on the presidency of Gen. Augusto Pinochet.

A written declaration by the 16-party opposition coalition said it had evidence that Pinochet supporters plan ''blackouts and clashes with the people to interfere in the delivery of results'' of the Wednesday referendum.

''We call on people to vote early and to remain in their homes, to reject provocations and violence, the only recourse available to the regime to create a situation of chaos that impedes the normal voting process,'' it said.

Church sources said privately they had learned of possible violence aimed at invalidating the results. Among those expressing concern is Bishop Carlos Gonzalez, president of the Chilean Episcopal Conference, the sources said.

Pinochet's name is alone on the ballot. If a majority votes yes, the 72- year-old general will begin a new eight-year term in March, but if most Chileans vote no an open presidential election is to be held next year, with power transferred in March 1990. Most polls indicate Pinochet will lose.

Socialist Ricardo Lagos, who read the opposition declaration at a news conference, would not describe the evidence of plans by pro-government elements.

An opposition source told The Associated Press it was based on the thefts of several buses identitical in make and model to those used by national police, and an army alert about supposed plans for widespread leftist terrorism on voting day.

He said national police officials, in conversations with opposition leaders, had said the buses might be painted police green and ''used in poor neighborhoods'' to provoke clashes with residents. Police discount the idea that leftists stole the buses, the source said.

National police issued a statement Monday saying six Mercedes and Ford buses ''similar to those used by the institution'' were stolen in Santiago alone in the past five months. ''These vehicles could be used to commit crimes against people and property, to be attributed to police or the armed forces,'' the statement said.

It urged people to inspect police buses and personnel to make sure they had the appropriate markings and identification.

According to the opposition source, a general revealed in conversation that the army was told to expect attacks by communist urban guerrilla groups on power lines and other targets. A church source confirmed the conversation.

Noting that leftist guerrilla groups declared a ''truce'' until after the referendum, the sources said the opposition and church leaders fear the army alert is designed to prepare soldiers for violence that actually would be carried out by right-wing groups, not leftists.

Pinochet, the army commander, seized power in September 1973, ousting the 3-year-old elected government of President Salvador Allende, an avowed Marxist who died in the coup.

Patricio Aylwin, president of the Christian Democratic Party, told another news conference the violence might be used as a pretext to declare a state of emergency and curfew, and to require that television and radio stations broadcast only officially approved information. Aylwin is an official spokesman for the opposition coalition.

In Washington, State Department spokeswoman Phyllis Oakley said: ''We have heard reports that the Chilean government has plans to cancel Wednesday's plebiscite or to nullify the result. We view them with serious concern. ... We have transmitted our concern directly to the government of Chile.''

A survey released Monday by the respected Center for Studies of Contemporary Reality gave Pinochet 20.8 percent of the vote and the opposition 54.4. A poll by the detective division of the national police showed the general ahead 52.7 percent to 47.3.

Police and military forces went on barracks alert Monday, a traditional election practice in Chile.

Soldiers began assisting police on street patrols Sunday, manning machine guns atop pickup trucks and other small vehicles. By law, campaigning ended at midnight Sunday.

Wednesday has been declared a national holiday.

A national police colonel told the AP he expects street disturbances Wednesday night.

''Regardless of the result, there will be problems,'' he said on condition of anonymity, and added:

''We are prepared to face any emergency whatsoever. I repeat, any situation, not only in Santiago but in other cities we consider potentially risky.''

He identified those as Antofogasta in northern Chile, the central port of Valparaiso, and Concepcion in the south.