WASHINGTON (AP) _ President Reagan hailed White House aide Donald R. Fortier, who died of cancer at age 39, for his creativity and his unflagging efforts to establish world peace.

Reagan said Sunday that as his deputy national security adviser, Fortier's ''creativity in the search for lasting peace throughout the world contributed significantly to our progress toward that goal.''

The president's statement, issued from his California ranch where he is vacationing with his wife, Nancy, praised Fortier for working ''tirelessly and brilliantly in developing our national security policy.''

''Nancy and I extend our heartfelt condolences to Don's wife, Alison, and his son, Graham. May God bless them,'' Reagan said.

Fortier, who had been ill since May with liver cancer, died Saturday night at Georgetown University Hospital, officials said.

Highly respected and well-read, Fortier was known inside the White House as an astute policy analyst with expertise on several regions of the world. He helped formulate the White House policy on Libya and was instrumental in reaching agreement for the sale of American nuclear technology to China.

He also was an architect of the so-called Reagan Doctrine, which includes aid to Latin American anticommunist groups.

Fortier was appointed deputy assistant to the president for national security affairs in 1983 under former national security adviser Robert McFarlane. He continued to serve in that position under the present national security adviser, Vice Adm. John Poindexter.

Previously, Fortier was the National Security Council director of Western European and NATO affairs and special assistant to the president on political- military affairs.

He joined the administration in 1981 as deputy director for policy planning at the State Department, and in 1982, was awarded the department's superior honor award for his contributions to U.S. foreign policy.

Before joining the executive branch, Fortier served as a senior adviser to the House Foreign Affairs Committee and a national security consultant to the RAND Corp.

He received an undergraduate degree from Miami University in Oxford, Ohio, and a master's degree in political science from the University of Chicago, where he held a Ford Foundation scholarship and did graduate work from 1971 to 1975.