Both players have until Nov. 30 to decide whether to accept the offers. If they decide to sign elsewhere, Oakland would receive draft-pick compensation next June.
Willingham is one of six players who is an exception to baseball's free-agent compensation rules this winter, under the terms of the labor deal signed by MLB and the union on Tuesday.
By offering Willingham arbitration, the A's could receive a high draft pick and a compensation-round pick in next summer's draft if Willingham signs elsewhere. They would pick just ahead of the team signing Willingham, but the team that signed him would not lose a draft pick -- a change from the old rules.
Willingham had career highs of 29 home runs and 98 RBIs in 2011, the most by an A's player since Frank Thomas' 114 in 2006, and likely will have plenty of suitors.
DeJesus batted a career-low .240 with 10 homers and 46 RBIs in 2011.
General manager Billy Beane has acknowledged it could be difficult to sign his own free agents given the team's unsettled ballpark situation. A's owner Lew Wolff wants to move the team to San Jose but is waiting for word from commissioner Bud Selig.
Information from The Associated Press was used in this report.