SÃO PAULO, Brazil — The American aerospace giant Boeing is eagerly pursuing a partnership with the Brazilian jet maker Embraer as part of a global battle with its European rival, Airbus.

But the talks, which moved into high gear late last year, are advancing at a politically fraught time in Brazil, and the Brazilian government — which owns a so-called golden share that gives it veto power over any change in ownership at Embraer — could derail a deal the two companies are said to be racing to complete.

A deal with Embraer would give Boeing a broader portfolio of aircraft, including, crucially, access to Embraer’s smaller regional planes, which compete directly with jets manufactured by the Canadian company Bombardier.

To prevail, however, Boeing will need to overcome political misgivings in Brazil, even though Embraer has a lot to gain.