In the biggest push yet to strengthen the nation's defences against bioterrorism, key senators yesterday introduced legislation aimed at providing $3.2 billion this year to help prevent, detect and treat terror-related health threats - more than double what President Bush has requested. The bill calls for stockpiling vaccines and antibiotics, strengthening the Centers for Disease Control and Prevention, beefing up food inspections, and giving state and local officials new resources for preparing for bioterrorism attacks. Even though Bush has resisted spending that exceeds his budget requests, Sen. Edward M. Kennedy (D-Mass.), who joined with Republican Sens. Bill Frist (Tenn.) and Judd Gregg (N.H.) in drafting the bill, said he believes the president will support the measure. Kennedy and Frist expressed confidence that it will be passed and signed into law before Congress finishes work for the year, probably by mid-December.