With a touch of humor, a barb for his critics and mention of America's destined role of world leader, President Reagan said goodbye to his top aides yesterday in a White House ceremony before departing for Europe.

"Who's tending the store?" a confident and apparently relaxed Reagan asked mischievously as he peered at an audience composed of members of the Cabinet, the Joint Chiefs of Staff and virtually all his other key advisers in the East Room.

Then, raising his head in the direction of the private residence of the executive mansion, he said, "Well, I think we've got everything packed, and Nancy is upstairs unplugging the toaster. I guess we're ready to go."

Reagan took the occasion to commend his aides for their work in carrying out his policies, and added: "I know that what we've been doing doesn't read well in The Washington Post or The New York Times, but believe me, it reads well in Peoria."

Reagan, who flew to Paris yesterday on the first leg of his 10-day trip, described his mission as carrying on the task of world leadership "this country never sought" but had thrust upon it at the end of World War II.

In brief remarks read from notes as he stood at a raised lectern, the president rejected what he described as the drift here and abroad from free trade and "toward protectionism," and he brushed aside views of those in this country "who yearn for the isolationist shell."

"If it is, as it appears to be, that we're destined to play a leadership role, then we shall do so with one purpose in mind, to affirm and protect the fundamental values of our people and the people of those countries that are allied to us in this determination to be free," he said.

Reagan said the United States and its European allies had "weathered threats of aggression and internal disagreements, but we've maintained a sense of unity and a commitment to freedom, and we're still being tested, possibly more now than ever before. It's important for that reason to meet and renew our bond."

Showing pride as he recalled his steps toward the announcement Monday that the United States and Soviet Union will begin strategic arms talks June 29, Reagan said he would be able to explain in detail to the Europeans "our plans for engaging the Soviet Union in realistic arms reduction talks."

The nuclear disarmament initiatives have helped raise his stock in Europe, particularly in West Germany where pacifist and antinuclear sentiment is strong and where Reagan's hawkish anti-Soviet rhetoric has caused deep concern.

Reagan seemed less sanguine, however, on what he could tell Europeans about U.S. economic conditions. The Europeans are frustrated by continuing high U.S. interest rates that encourage a flight of capital from their countries to higher-yielding investments in this one.

The president did not mention interest rates, choosing instead to emphasize reducing worldwide inflation, the one key economic indicator that has improved during his tenure.

At Orly Airport outside Paris last night, the Reagans were met by French Foreign Minister Claude Cheysson and their host, U.S. Ambassador Evan Galbraith, but a welcoming ceremony was rained out.

Reagan is to attend a seven-nation economic summit at Versailles, France, beginning today and a 16-nation NATO summit in Bonn next week. His itinerary includes Rome, London and Berlin.