Lopez had a breakout season in 2009-10, playing in all 82 game and averaging 18.8 points and 8.6 rebounds per game. He was 10th in the league with 1.7 blocks per contest. He was an all-rookie selection in 2008-09. The Nets picked up the fourth-year option for Lopez, the 10th overall pick in the 2008 draft.
Williams, the 11th selection in 2009, averaged 8.4 points and 4.5 rebounds per game last season.
Lopez will earn $3.0 million in 2011-12, while Williams will get $2.3 million.
The Nets finished with the worst record in the league last season at 12-70 but have had a busy offseason. Russian billionaire Mikhail Prokhorov is now the owner, while Avery Johnson takes over as coach and Billy King as general manager.
The Nets selected young forward Derrick Favors with the third overall pick in the draft, but then got involved in talks that would have sent him to Denver in a trade for Carmelo Anthony. That deal has cooled off.
Information from The Associated Press was used in this report.