The arrival of U.S. Special Forces trainers in this battered town last month signaled the beginning of a change that gives the United States more direct military involvement in Colombia's long civil war and could lead the country's two leftist guerrilla armies to broaden attacks against U.S. targets.

Late last month, the smaller of the two Marxist-oriented guerrilla movements, the National Liberation Army, kidnapped two journalists, a Briton and an American, in this oil-rich region of eastern Colombia, saying the province had become a "war zone declared by the North American government and the Colombian state."

Although meant as an explanation for the abduction of the journalists, who were released Saturday after 11 days in rebel hands, the warning stirred deep anxiety among Colombian civilians that the presence of U.S. troops would prompt a sharp response from the guerrillas.

Over the course of this year, Arauca province is scheduled to become the center of gravity for a $470 million-a-year U.S. effort to help President Alvaro Uribe cripple the enduring leftist insurgency by strengthening Colombia's military. The training program will emphasize counterinsurgency rather than the anti-drug techniques that had been the focus of U.S. aid to date.

In expanding the training beyond counter-drugs, the United States has abandoned an ambiguity that was once carefully cultivated by U.S. officials, promising to make the United States a higher-profile player in Colombia's 39-year-old war.

This month, U.S. officials will begin shifting military resources previously used in anti-drug operations in southern Colombia to this province, which lies on the Venezuelan border and is 220 miles east of Bogota, the capital. Helicopters will be used directly against the two guerrilla armies, which the State Department considers terrorist organizations. Under the program, the Colombian military is scheduled to buy additional helicopters and other military equipment.

The effort has been presented as a way to help Colombian troops protect an economically important government oil pipeline from guerrilla attack. But it is clear from the training taking place on an army base here that defending the pipeline will mostly entail offensive operations against the seasoned guerrillas who have prospered on this swampy stretch of oil and coca fields. The first military unit selected for training, for instance, is a counter-guerrilla battalion, not a unit whose principal task is to protect the pipeline.

"I look at this [program] more as one that is trying to establish security in an area where there just happens to be a pipeline," a U.S. official said.

The 70 U.S. trainers in Arauca -- more than half here, the rest on nearby bases in Cano Limon and Arauca city to the east -- are a useful propaganda symbol for the guerrillas, who have long warned of U.S. economic designs on Colombia's natural wealth. The message has resonated all the more as the United States prepares for a possible war in Iraq that could disrupt world oil supplies.

In the coming weeks, U.S. officials say, at least five UH-1H Huey II helicopters will be sent from the south to support counterinsurgency here. Those helicopters, funded under a $1.3 billion U.S. anti-drug package, were restricted to anti-drug operations until the Bush administration received congressional approval last year to allow their use in counterinsurgency.

U.S. officials say that at least five helicopters will be needed to meet their initial goal of being able to move a 40-man platoon to guerrilla targets at one time. They say the $88 million to $98 million program will pay for as many as 10 new helicopters, "target acquisition" systems, night-vision gear and the training itself.

About 25 U.S. trainers will remain in Larandia, an army base in southern Colombia, preparing troops to carry out operations against drug labs and coca crops. In addition, 15 U.S. trainers based in Tolemaida, west of Bogota, are preparing a 300-man commando battalion to be used to hunt important guerrilla commanders and destroy guerrilla command-and-control centers, small-unit capabilities the army does not have. The U.S. trainers are not authorized to participate in military operations.

On a gray morning here last week, troops from the 30th Counter-Guerrilla Battalion based in Fortul, 12 miles south of Saravena, gathered in small groups to begin the 10-week course on "how to move, communicate and shoot," in the words of one U.S. official. U.S. officials hope to train two battalions of the 18th Brigade, about 800 men, this year.

Saravena, a city of 40,000 residents, once dominated by guerrilla militia networks, offers a surreal picture of Colombia's war. Despite the oil riches that surround the city, the urban centerpiece is a bombed-out police station and city hall, the rubble lined with sandbags and gun emplacements. The airport, destroyed last year by guerrilla attacks, remains decorated with signs sponsored by the chamber of commerce that cheerfully invite passengers to return soon.

The National Liberation Army, a 5,000-member Cuban-inspired insurgency known by its Spanish initials, ELN, has profited from the oil pipeline, which runs 500 miles from Cano Limon to Covenas on the Caribbean coast. In general, the ELN bleeds funds from sympathetic nonprofit organizations and city halls that get extra taxes and subsidies from pipeline royalties.

The ELN's larger cousin, the 18,000-member Revolutionary Armed Forces of Colombia, or FARC, has moved in more recently seeking its own share of the royalties.

Both guerrilla groups have declared U.S. interests in Colombia military objectives, but they have usually reserved their attacks for helicopters, anti-drug spray planes and economic infrastructure. The notorious exception was the FARC's 1999 killing of three American indigenous-rights activists in Arauca, the result of a power struggle between the guerrilla groups.

The most prominent guerrilla target has been the pipeline, jointly operated by the government and Occidental Petroleum Corp. of Los Angeles. The guerrillas, primarily the FARC, blew up the pipeline 170 times in 2001, according to the state oil company, Ecopetrol. According to military officials and provincial politicians, the objective of most of the bombings was to force the ELN to share more of the proceeds.

The attacks cost the government $500 million in revenue in 2001, money the United States wants Uribe to be able to invest in the war effort. Bombings dropped to 42 last year with better security and a guerrilla agreement over money.

Uribe last week ordered that Arauca's oil royalties, amounting to roughly $42 million a year, must be managed by his administration rather than by the provincial government, a move designed to choke off the ELN's financing. That announcement angered regional political leaders, who say not a penny of promised social aid has arrived since September, when Uribe declared the region a special security zone.

"It's a way to generate news," said Jose Trinidad Sierra, Saravena's mayor. "The question is: Does it work? And what comes next? Beyond these Special Forces, what the government must do is invest in employment."

Several human rights, political and military officials here said the kidnapping of the two journalists, on assignment for the Los Angeles Times, broke the long-standing immunity enjoyed by foreign journalists working in Colombia and marks a change in guerrilla tactics.

Scott Dalton, 34, a photographer from Conroe, Tex., and Ruth Morris, 35, a British citizen raised in Los Angeles, were detained at an ELN roadblock Jan. 21 as they traveled from here to Tame, 35 miles to the south.

The two were released Saturday without fanfare to an International Red Cross delegation not far from where they were originally seized.

"It's a deplorable act, but it is the result of anger among the people here over the militarization of Arauca," said Jose Murillo, president of the Joel Sierra Regional Committee for Human Rights. "You don't need some deep analysis to tell you what the U.S. troops are going to bring, a worsening of the government's dirty war against the left."

U.S. Special Forces trainers in eastern Colombia will emphasize counterinsurgency tactics over anti-drug activities.