President Reagan, preparing to fly to California today for his annual yuletide vacation, said yesterday that his administration has tried to foster "the spirit of generosity" that is evident during the holidays.

In his weekly radio address Reagan said "the spirit of good will and benevolence" is alive despite a reported drop in charitable giving in the midst of economic anxiety.

Reagan said that since 1980, charitable giving in the United States increased 77 percent from $49.08 billion to $87.22 billion in 1986.

"That spirit of generosity that is so evident during the holiday season is something we've tried to foster during the past seven years of this administration," Reagan said.

Reagan, who has sought to reduce domestic spending for government social programs and to encourage voluntarism, said: "I don't think there's any better gauge for the soul of a nation or the essential goodness of a people than an accounting of their personal involvement in helping others, either through donations of money or time. And voluntarism is still a strong force in communities throughout our country."

But the holiday season has brought reports of a slump in contributions to charitable organizations, attributed by some analysts to the financial reverberations of the stock market plunge of Oct. 19, which is under study by a presidential commission headed by Wall Street analyst Nicholas Brady.

"There is always much to improve," Reagan said. "But I can assure you that the spirit of good will and benevolence -- an aspect of our national character recognized since the early days of our republic -- remains a vibrant part of the American way of life."

Declaring the spirit of neighbor helping neighbor to be "part of our national character," Reagan singled out three Americans for exemplary volunteer efforts:Engineer Bob Carver of Vicksburg, Miss., who has spent the past five Christmas seasons raising more than $20,000 for the Salvation Army to buy toys and food for the needy, send children to summer camp and pay utility bills for the elderly. Ruth Heywood, 74, of Casa Grande, Ariz., who annually solicits grocers for food and utensils and arranges for Thanksgiving and Christmas meals to be delivered to the homebound and disadvantaged. Elementary school teacher David Rayl of Bald Knob, Ark., who Reagan said plays Santa to "hundreds of needy families" through "hard work and private and corporate donations."

"Most of us know someone like Bob Carver, Ruth Heywood or David Rayl," he said. "Down deep, who cannot respect such heroes? I'd like to think there's a little of them in each and every American."

In the Democratic response to Reagan's radio address, Rep. Dale E. Kildee (D-Mich.) said Congress hopes to work closely with Reagan during his last year in office to achieve "great progress for human dignity."

Reagan and his wife, Nancy, will travel to the West Coast today to spend two days with family and friends in Los Angeles before flying to Palm Springs, where they will stay until Jan. 3.