MOSCOW  President Hugo Chávez of Venezuela and President Dmitri A. Medvedev of Russia declared Tuesday that their countries would more closely coordinate their actions on global oil and gas markets and that they would work together on foreign policy, a sphere in which both countries have sought to counter American influence.

Mr. Chávez, who was also expected to sign contracts to purchase more than $1 billion worth of Russian arms, called for the two nations to become “strategic partners” to defend against what he called an American threat to his country.

“That will guarantee the sovereignty of Venezuela, which the United States is now threatening,” Mr. Chávez said, according to the official Russian news agency RIA-Novosti, at the start of two days of planned meetings.

Mr. Medvedev, who met Mr. Chávez for the first time since succeeding Vladimir V. Putin as president, stopped short of endorsing his guest’s sharp remarks about the United States. So did Russian officials, who stressed the business significance of the new cooperation, including three new deals to expand Russian oil and gas companies’ presence in Latin America, rather than its political import.