Berkman, a switch-hitter, would serve as a DH and occasional first baseman. He would waive his no-trade clause for the Yankees without requiring the team to pick up his $15 million club option for 2011, the source said.
Berkman, 34, is batting a career-low .245 with 13 homers and 49 RBIs.
Because of Berkman's 10-and-5 status, a trade to the Yankees would not become official until after the expiration of the 24-hour window.
A source said Berkman gave his approval earlier today, but official word of the trade would not come until Saturday afternoon.
Berkman can change his mind at any point during the 24-hour window, but the source doubts that will happen.
A Berkman trade to the Yankees could put the Nationals in bind with Adam Dunn. The Nats would lose a big potential suitor. The WhiteSox can hold out for a deal to their liking. The Rays can't be sure Dunn will succeed as a DH after their failed expriment with Pat Burrell. So the Nationals might be stuck without a deal for their slugging first baseman.