All three said they will not hire agents, which allows them to withdraw before the May 25 NCAA deadline to return to school for their final seasons of eligibility.
Hawkinson, a 6-foot-10 forward, averaged 15.4 points and 11.1 rebounds per game last season, both team highs. Iroegbu, a 6-foot-2 guard, averaged 12.7 points and 3.6 assists. Clifford, a 7-foot center, averaged 6.8 points and 2.1 rebounds in his first season with the Cougars.
Washington State was 9-22 last season and 1-17 in Pac-12 play.
The Associated Press contributed to this report.