Washington, D.C. ? Some of the nation’s biggest banks are in for a windfall – on top of the $700 billion government bailout – thanks to a new tax policy quietly issued by the Treasury Department.

The notice gives big tax breaks to companies that acquire struggling banks hit hard by the mortgage crisis. In some cases, the tax breaks could exceed the cost of acquiring the banks, according to analyses by private tax experts.

The change could cost the Treasury as much as $140 billion by enabling firms that acquire struggling banks to use more losses incurred by those banks to offset their own taxable profits.

Wells Fargo & Co., which made a bid to acquire Wachovia Corp., just days after the notice was issued, stands to reap about $20 billion in additional tax savings because of the change, according to the analyses. Wells Fargo paid $14.8 billion in a stock deal to buy Wachovia.