D.C.'s Bishop, Cook, Purcell & Reynolds is talking merger with the 400-lawyer firm Winston & Strawn, the oldest law firm in Chicago.

The two haven't quite reached the altar yet, but they've started the long walk down the aisle, according to the managing partners of both firms.

Winston & Strawn once had a 40-lawyer outpost in Washington, in the days when former vice president Walter F. Mondale ran its operation here. But Mondale departed for practice in Minneapolis in 1987, and now Winston & Strawn is down to about 20 lawyers.

The firm has been scouting talent for a D.C. expansion for some time, and the fit looks right with Bishop, Cook, according to Winston & Strawn's Gary L. Fairchild.

Winston & Strawn could use Bishop, Cook's prominent practices in energy and solid waste and environment. The mid-size D.C. firm, with its 85 lawyers, would win the depth in corporate and litigation work that comes with a 400-lawyer firm.

And, noted J. Michael McGarry III of Bishop, Cook, , the new firm could tout two former U.S. attorneys on its roster: Joseph E. diGenova, who joined Bishop, Cook after leaving that post here, and former federal prosecutor Dan K. Webb of Chicago.

If all goes well, the two firms hope to consummate the marriage by September.