A bomb explodes outside the U.S. ambassador's residence in the early morning. A policeman is killed in a shoot-out with armed Communists at a bakery. Another is kidnaped and held for three days. Blasts occur outside government offices, in front of banks and businesses, along railroad tracks, under electricity pylons and inside buses and cars.

These incidents, all of which took place last month in Chile, reflect a steady campaign of violence by Communist militants to wear down the military government of Gen. Augusto Pinochet. They are the reason Pinochet gives for staying in power and, in the process, restricting public assembly, denying free elections, restraining the media and ordering mass detentions and neighborhood raids.

But rather than curbing terrorism, Pinochet's harsh repression and economic failures have provoked it, providing fertile ground for leftist organizers, according to analysts here. Many Chileans say that Pinochet has been breathing new life into the Communist Party after its virtual demise following the 1973 coup against Salvador Allende's Marxist coalition.

In the name of fighting internal subversion, the size of Chile's armed forces has been increased from 60,000 to 101,000, a jump of 67 percent, since the military took power 13 years ago. But the Communist Party has grown, as well, drawing new members from two areas where it used to be weak: the universities and the slum communities surrounding Santiago and other cities.

Today, the Communists are the second best organized party in Chile, according to diplomats and Chilean politicians; the centrist Christian Democratic Party ranks first.

"Politically, the Communist Party was out of the race after 1973," said Orlando Saenz, who headed the national industrialists' association in Allende's time and supported the coup. "Pinochet has revived it in the past 13 years. It is now a strong group."

How strong is still a guessing game in the absence of elections. But opposition politicians here estimate that the Communists could draw as much as 20 percent of the popular vote. They captured 16 percent in 1970, as a member of Allende's Popular Unity coalition.

U.S. officials, concerned about Communist gains, have stepped up pressure on Pinochet to return Chile to democracy before the country erupts in social chaos, a situation the Communists are well positioned to capitalize on. U.S. Ambassador Harry Barnes, despite his publicized opening to the Chilean opposition, has so far avoided meeting Communist representatives.

Today, Pinochet and the Communists seem to feed off each other.

"Though their objectives are diametrically opposed, the military government and the Communist Party have a relationship of mutual dependence," observed Andres Allamand, leader of the center-right National Union Movement. "To justify repression, Pinochet always mentions the outburst of terrorism. To justify confrontation, the Communists always cite increased repression as proof that the military government intends to perpetuate itself."

A resident foreigner, discussing how to diagram Chile's complex array of political parties, suggested the chart be drawn not in a straight line from one side of the political spectrum to the other, but in a horseshoe shape, so the two extremes approach one another.

Chilean Communists came only recently to support violence as a political tool. Under Allende, they acted as a restraining force against the president's more militant Socialist Party and other leftist groups in the coalition. Rooted in the mining and construction unions, the party, which was founded 64 years ago, followed the Soviet line and worked through parliament rather than fighting in the streets.

After the coup, the Communists retreated and concentrated on reconstructing their decimated ranks underground. Some moved abroad. Luis Corvalan, the general secretary, went to Moscow and is still there, retaining the title of leader of the Chilean party.

The leadership inside Chile is clandestine, but the party has several members who act openly as spokesmen. A number of Chileans publicly identify themselves as Communists. Of the 45 persons who belong to the party's policy-making Central Committee, "not more than 10" live outside Chile, according to Patricio Hales, a party spokesman.

"Communism is not a party but a culture in Chile, a large family that shares a vision of the world, a set of values," said Augusto Varas, a political scientist at the Latin American Faculty of Social Sciences. "They fight and suffer together. They have gone through a long process of homogenization, like the military and the church."

In 1980, the party took a turn toward extremism, declaring support for "all forms of struggle." The new militancy was a response to the adoption that year of a constitution that concentrated power in the president and effectively ensured the armed forces of control until the next century.

Two other factors are thought to have pushed the Communists to endorse violence. First, the Sandinista victory in Nicaragua became a persuasive model to Latin American Communists of a successful armed struggle against dictatorship. Second, Chilean Socialists had gone through their own soul-searching after the coup and emerged more moderate, embracing democracy and repudiating Marxism-Leninism and the violent road to power.

The Manuel Rodriguez Patriotic Front appeared in 1983 and started claiming responsibility for political assassinations, kidnapings and sabotage. The armed group has an ambiguous relationship with the Communist Party. Both organizations deny formal links, but the front is largely staffed with Communist youths and often prints its propaganda on the same underground machines used by the Communist Party.

Reuter reported the following:

Chile's military government has warned foreign legislators planning to attend an opposition-sponsored conference here next week that it cannot guarantee their personal security, diplomats said Saturday.

The warning was contained in a notice from the Foreign Ministry delivered to embassies Friday afternoon.

It said the government of President Augusto Pinochet had information that the meeting could produce hostile demonstrations and terrorist attacks and that it could not guarantee the visitors' security. Some diplomats said they saw the note as a veiled threat.