Mr Chavez said Russia and Venezuela would cooperate in various fields
Hugo Chavez has called for a strategic alliance with Russia to protect Venezuela from the US.
The Venezuelan president's call came as Moscow and Caracas agreed to extend bilateral co-operation on energy.
Speaking during a two-day visit to Russia, Mr Chavez said oil and military cooperation were vital to guarantee Venezuela's sovereignty.
Russian President Dmitry Medvedev said three Russian energy companies are to be allowed to operate in Venezuela.
He gave no details of an anticipated arms deal between the two countries. But Mr Chavez seemed upbeat about the prospect of military co-operation.
"If Russia's armed forces want to be present in Venezuela, they will be given a warm welcome," he told a news conference after the meeting.
He said Venezuela would pursue new Russian arms deals "because the North American empire... has plans to invade Venezuela, to disarm Venezuela".
Venezuela's president said he had felt "strong human warmth" during the meeting with his Russian counterpart, adding that "personal chemistry immediately appeared between us".
Mr Chavez held warm talks with Russian Prime Minister Vladimir Putin
"We are considering issues linked to our strategic partnership, be it in the energy sector, industry, finance, science and technology, or military issues," said Mr Chavez.
Following the talks, Mr Medvedev said Gazprom, Lukoil and TNK-BP would be allowed to operate in Venezuela's resource-rich Orinoco Belt.
"Venezuela is now the most important partner of the Russian Federation," said the Russian president, a former chairman of Gazprom.
He said a proposal to create a group of leading gas producers similar to the oil cartel, Opec, had not been abandoned.
During his stay in Russia, Mr Chavez also held warm talks with Russian Prime Minister Vladimir Putin, focusing on economic and military co-operation.