The moves temporarily secure the players' rights, though it's unclear what their status will be under a new collective bargaining agreement after the current one expires on Thursday night.
Tight end Scott Chandler was also tendered a contract by the Bills on Tuesday.
Whitner completed a five-year contract last season, and questioned whether he'd return to Buffalo after negotiations broke down in December. Posluszny completed a four-year deal and has said he's open to re-signing with the Bills.
Chandler joined the Bills in December after being claimed on waivers from Dallas.