By Frank Jack Daniel

LA ORCHILA, Venezuela, June 6 (Reuters) - Venezuela test-fired missiles in the Caribbean Sea on Friday in a display of military strength at a time of tense relations between Washington and leftist President Hugo Chavez.

Five Russian Sukhoi fighter jets swooped over the military base on the island of La Orchila, dropping a half-tonne bomb and firing a KH-59 missile at a seaborne target. A patrol boat fired an Otomat surface-to-surface missile at the same target.

Air Force Commander Gen. Luis Jose Berroteran, said the newly acquired military equipment would help Venezuela ward off potential invasions.

"When you have (resources) that are desired by foreign powers, you have an obligation to your people to defend them," he said.

Chavez frequently accuses the United States of plotting his overthrow to snatch the OPEC nation's oil reserves, and in recent weeks has said the U.S. attitude toward Venezuela echoes U.S. "aggression" in Iran and Iraq.

The test was the first display of firepower purchased from Russia and China using profits from its record oil revenues.

Washington has criticized Chavez's military buildup, arguing it could destabilize the region. Chavez bought the Russian fighter jets after the United States blocked his efforts to buy planes with U.S. technology.

Venezuela has the fourth-largest military budget in Latin America, and analysts say its military spending is relatively low in relation to its GDP.

Tensions remain high between the United States, Venezuela and its neighbor, U.S.-ally Colombia, which accuses Chavez of helping Marxist insurgents fighting the government.

This week, U.S. Ambassador to Venezuela Patrick Duddy said relations between the two countries were going through "very difficult times."

Chavez sees a U.S. plan to relaunch its fourth naval fleet in the Caribbean after nearly 60 years as a threat and says incidents such as the violation of Venezuela airspace by a U.S. warplane in May are evidence of hostility.

"We are threatened by the empire. What do they want, that we disarm?," he said in May after the airspace incident, which also took place near the La Orchila base, home to a presidential retreat.

"We are not going to harm anybody, but nobody should make mistakes with us."

Increased weapons budgets in South America have prompted talk of an arms race in the region, but most analysts say the spending so far is justified after years of defense neglect.

Caracas-based security analyst Rocio San Miguel says Venezuela needs to modernize its military to adequately control its vast land and maritime borders.

"It is legitimate that a state renew its arms systems, and in Venezuela this is a necessity," she said. "The challenge is (to ensure) these acquisitions do not turn into threats to our neighbors." (Editing by Brian Ellsworth and Stacey Joyce)

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