In a speech marking the 12th anniversary of the bloody coup that brought him to power, Chilean President Augusto Pinochet took a hard line today on a church-backed plan for a return to democracy.

Gen. Pinochet demanded that opponents show they are interested in more than mere "conquest of power" and that attractive rhetoric be backed by "honest deeds."

In a 90-minute speech before about 2,000 military, diplomatic and governmental guests, the president lashed out at critics, saying, "Their anxiety for reaching power at any price makes them try to destabilize the government."

Pinochet said Chile would achieve "true democracy" only by adhering to the terms of an authoritarian constitution he pushed through in 1980 and seemed to step back from a more conciliatory position offered by officials last week on the opposition parties' proposal.

However, Pinochet, did not reject outright the proposed "national accord," as the 11-party agreement signed last month is known. Worked out under the sponsorship of Roman Catholic Cardinal Juan Francisco Fresno, it united opposition groups from across the political spectrum in a call for elections -- although with no date specified.

Fresno is said to have stepped in to promote the agreement among the parties in an effort to head off spiraling street protests and political violence that have taken dozens of lives within the past year. The cardinal did not attend the diplomatic gathering. According to an unofficial church account, he stayed away after being informed of the response Pinochet would deliver.

Pinochet did say that among the signatories were sectors that "might have relevant opinions on the institutional development" of Chile, but only if they could show they were interested in more than "just the mere conquest of power."

It was unclear whether these words reflected a subtle shift by the government toward negotiations with civilians. One theory was that the phrasing was part of a government effort to fragment the opposition by signaling a willingness to deal only with the more conservative parties.

"We cannot accept that behind a supposed democratic objective there is the expression and the advance of totalitarian communism," he said. "Some of those who signed this are responsible for the strategy designed to make Chile a mere satellite of the Soviet Union." The Communists were not a party to the accord, but the Marxist Socialists were.

Pinochet also lashed out at non-Marxist parties that, he said, "abandoned their principles" to make alliances against his government.

The opposition's proposal picked up another supporter last night in retired Air Force general Gustavo Leigh. He was a member of the original junta who stepped down several years ago after differing with Pinochet.

Pinochet said Chile was the only nation in history to liberate itself from "Soviet communism," and that because of this his country was the victim of unremitting attacks by groups "that will not accept defeat."

The general said his government attaches special importance to the U.S.-Chilean relations, which he said were based on "friendship, cooperation and mutual respect." He did not comment on the fact that the State Department recently praised the church-backed proposal for a return to democracy.

Santiago was blacked out twice tonight. A progovernment radio station said two power pylons near Santiago had been blown up. Four persons were reported injured in clashes with police in the poor neighborhood of La Legua and seven in the slum district of La Victoria.

At least 30 persons were detained while attempting to hold memorial ceremonies for Socialist ex-president Salvador Allende, who died in the presidential palace during the 1973 coup. Among those arrested was Fabiola Letelier, a sister of Orlando Letelier, a minister in Allende's Cabinet who was assassinated in Washington in a bombing laid to agents of Pinochet's government in 1976.