When the Broncos take the field against the Green Bay Packers, there will be more at stake than Denver’s first Super Bowl win in five tries: The fate of a new stadium, whose financing depends on ballot approval of a sales-tax extension, could hang in the balance. In early 1997, polls showed community sentiment running strongly against a publicly financed new home for the Broncos. But now, in the euphoria of a 12-4 season record and three play-off wins, Denverites seem ready and willing to tax themselves for the even greater glory of their gridders. In fact, according to a survey, those in favor now outweigh those opposed 55 percent to 38 percent. Of course, before the project can start, Denver’s city council must permit the Broncos to break their lease on existing Mile High Stadium. To smooth the way, a team lobbyist has been offering Super Bowl tickets to the 13 council members at the nearly impossible to get face-value price of $275, way below the going street rate of $1,000 plus. Last week several members of Denver’s ruling body did not seem unwilling to avail themselves of some bargain seats. But if the Broncs blow it, all bets are off.