SCENARIOS: How far will Colombia-Venezuela crisis worsen?

BOGOTA (Reuters) - Venezuelan troops this week blew up two makeshift bridges spanning the frontier with Colombia in the latest incident to stoke tensions between two South American neighbors caught up in a long dispute.

Relations soured further after President Hugo Chavez urged army commanders to prepare for war. The leftist says a Colombian plan to allow U.S. troops more access to its bases sets the stage for U.S.-backed attack against his OPEC nation.

While in the past Chavez and President Alvaro Uribe managed to pull back from the brink, most analysts say the current crisis will be more difficult to resolve and acutely raises the risk of a violent incident on the border.

Here are some possible scenarios in the dispute:

SMALL-SCALE BORDER INCIDENT, ACCIDENTAL CLASH

While robust bilateral trade in the past acted as a deterrent, security experts and analysts say there is now an increased risk of a clash along the frontier where both countries maintain a strong military presence. Belligerent rhetoric, illegal armed groups, increased military presence and protests over border closures create a volatile cocktail.

With little communication between the governments, an accidental exchange of gunfire or a clash spilling over from an unintentional border incursion are more likely than a planned assault, analysts say. Violence could also flare from an incident involving an illegal armed group such as Colombia's FARC rebels. But any confrontation will be sudden, small-scale and quickly contained.

"Our current assessment is that the possibility of a clash is very real," said Christian Le Miere, editor of Jane's Intelligence Weekly. "More likely will be some kind of clash along the border, either through regular forces or perhaps involving irregular forces such as the FARC."

SIMMERING TENSIONS AS ELECTIONS APPROACH

With both Colombia and Venezuela holding elections next year, analysts expect tensions to simmer as the two governments engage in an Andean-style "Cold War". Diplomatic exchanges and accusations of espionage will likely keep relations sour.

Chavez may want to ward off criticism over domestic problems such as high inflation and power and water shortages that have hit his popularity and shore up support before legislative elections in September 2010. Presenting Colombia as an aggressor backed by "imperialist" Washington may bolsters his image as a flagbearer of anti-U.S. sentiment.

Venezuelan officials have used recent violence along the border to hammer opposition politicians who control frontier states. Governors say that is just propaganda tactics.

Uribe, mulling a possible reelection next year, may also gain points from tensions as many Colombians still see him as a steady hand in dealing with the country's security situation.

FULL-BLOWN CONFRONTATION

Despite aggressive words, there is little appetite on either side for an full-blown conflict. Both governments -- Chavez more than Uribe -- may have domestic reasons for keeping tensions high. But full-scale confrontation would bring little political gain. Still, Colombia's armed forces are more geared up for dealing with its guerrilla insurgency rather than a border war. Chavez has built up his armed forces with modern Russia military hardware, including high-performance Sukhoi fighter jets that give him air superiority. But wider conflict also risks drawing in the United States.

"It is unlikely to spiral out of control so the maximum we now envisage is that we have some kind of small-scale military conflict that will be contained relatively quickly," said Christian Voelkel, a risk analyst at IHS Global Insight.

INTERNATIONAL MEDIATION

The Organization of American States is urging talks and Brazil has offered to negotiate an end to the crisis. Brazil's President Luiz Inacio Lula da Silva has invited the presidents to a summit. But the two sides seem more entrenched than in past disputes when they were able to resolve their differences with handshakes and a face-to-face meeting now looks unlikely.

(Reporting by Patrick Markey in Bogota, editing by Anthony Boadle)