The U.S. Tennis Association announced the seedings Wednesday, strictly following this week's WTA rankings.
Azarenka, who won the Australian Open in January, is followed by No. 2 Agnieszka Radwanska, the runner-up to Williams at Wimbledon last month.
Defending U.S. Open champion Sam Stosur is seeded seventh, and three-time winner Kim Clijsters is No. 23.
Venus Williams, who won the Open in 2000 and 2001, is ranked 47th and is unseeded.
The USTA said Tuesday that Roger Federer is seeded No. 1 among the men.
The draw is Thursday. Play begins Monday.