The Reagan administration, after 2 1/2 years of close and uncritical relations with Chile's military dictatorship, is trying actively to prod President Augusto Pinochet toward restoring democratic rule, U.S. officials said yesterday.

Signs of the policy shift have been evident in State Department comments this week on the mass protests that have gripped Chile. On Monday, department spokesman John Hughes sharply criticized the Pinochet regime's "detention and solitary confinement of prominent democratic leaders."

On Wednesday Hughes added, "We believe the current political tensions in Chile can best be resolved peacefully through moderation and dialogue regarding national issues, such as the transition to democracy."

The administration also has sought to encourage other Chilean institutions in maintaining independence from the government. Hughes Wednesday greeted the news that a Chilean court had ordered the release of Gabriel Valdes, president of the Christian Democratic Party, and other detainees by saying: "The court's decision is an indication that peaceful dissent is protected by Chilean law."

Administration officials, who asked not to be identified, said Hughes' remarks were not simply a reaction to the current unrest. Rather, they said, the public criticism is part of a month-old campaign to serve notice that the United States believes the Chilean military must start easing its repressive rule.

This shift, which the officials said has the approval of the White House and the top echelons of the State Department, was described as having resulted from several factors. Chief among them, the officials noted, is U.S. analysts' growing feeling that a failure by Pinochet to shift course could cause internal upheavals leading to civil war.

In addition, the sources said, there is a growing conviction here that Chile is becoming a test for President Reagan's argument that human rights abuses can best be curbed through quiet diplomacy and persuasion rather than by the highly publicized, activist approach applied to Chile under President Carter.

The officials acknowledged that the White House in particular has been motivated by concern over comparisons between its tough line toward the communist military regime in Poland and its tendency to soft-pedal excesses by the rightist Pinochet government.

As one official noted, "There simply hasn't been the shift toward moderation and democratization that we had hoped for. These guys the military are their own worst enemies. They are only deepening the resentments and divisions within Chile, and, in the process, they are making it appear that the United States has a hypocritical double standard when it comes to dealing with human rights questions."

The result was a decision to move in what one official called "subtle, incremental steps" to make clear that Washington is disappointed with Pinochet's course and to encourage the more moderate elements in the Chilean military to put their influence behind an accelerated timetable for returning to democracy.

"This is no big Carter-type push," one official cautioned. "We don't believe that Pinochet is in imminent danger of falling, and we do believe that, in one form or another, the military will be in control for some time to come. So it would be counterproductive to make a lot of noise that would give the impression of interfering in Chilean affairs. That would only undermine the moderates."

But, the officials insisted, the Chilean government is being left in no doubt about U.S. views. In addition to the statements here, the U.S. ambassador in Santiago, James Theberge, has spoken out on the need for democratization.

As a carefully calculated signal, he recently met with a group of dissident labor leaders at his residence at a time when the government had ordered the dissidents' arrest for seeking to promote a strike.