LA PAZ, Bolivia  President Evo Morales’s leftist government, which has asserted greater control over some of South America’s most coveted natural gas reserves, is facing a challenge as neighboring countries move to achieve energy security by cutting their dependence on Bolivian gas supplies.

New gas projects in Brazil and Argentina have come on line at a time when Mr. Morales is winning plaudits for a strong economy. It grew 3.7 percent last year, enabling him to consolidate control over energy resources, including natural gas, South America’s second-largest such reserve after Venezuela’s, and huge lithium deposits.

But even as Mr. Morales has emerged as one of the region’s strongest leaders, bolstered by a landslide re-election victory in December, concern is surfacing here over Bolivia’s long-term financial underpinnings as its neighbors start importing gas from distant sources like Qatar, and not so distant ones, like Trinidad and Tobago.

The reorganization of South America’s energy relationships is being closely followed by countries trying to limit their reliance on energy-rich nations that are in political flux or that use their resources as a political lever, as Russia’s state energy company has bullied former Soviet republics and Europe.