Two days ago, he said with a smile, he was "sitting in a hot pool" with the U.S. secretary of state, "philosophizing about the world and the sky."

Today, he was beside a mountain lake near this northern California resort town, surrounded by some of America's most important bankers, builders, lawyers and politicians, listening to Henry A. Kissinger discuss the "Challenge of the 1980s."

It is just another summer vacation for Helmut Schmidt, 63, chancellor of West Germany and the world's leading devotee of the geopolitical busman's holiday.

Last year Schmidt vacationed on a small island off Florida. This year it is Houston, Stanford, San Francisco, the Bohemian Grove and Vancouver, British Columbia.

When he's not visiting his little lakeside retreat in northern Germany, Schmidt loves to spend his spare time in the United States, escaping the routines of ceremony and office in his ninth year as chancellor as well as developing a relationship with Americans matched by no other European leader.

From years of U.S. vacations and cross-Atlantic contacts, Schmidt has become old friends with George P. Shultz. The two men arranged months ago to get together at the summer camp for U.S. corporate and political giants near here, the Bohemian Grove, a somewhat controversial retreat that bans reporters and women. It is further proof of Schmidt's sound choice of holiday companions that in the meantime his host has become secretary of state.

Schmidt and Shultz, along with Lee Kwan Yew, prime minister of Singapore, today rode by limousine the 150 miles from Shultz's home on the Stanford University campus to this resort area, Schmidt's second visit to the annual two-week Bohemian Grove encampment.

Former secretary of state Alexander M. Haig Jr. is here, but Defense Secretary Caspar W. Weinberger canceled at the last minute because of the tense Middle East situation, and President Reagan, although also a Bohemian Club member, has not shown up.

Schmidt is expected to spend tonight and Saturday night at the Grove's Mandalay camp, one of the several rustic lodges. Mandalay members include Shultz, Shultz' former employer, Stephen D. Bechtel Jr., former secretary of state Kissinger, former president Gerald R. Ford, Attorney General William French Smith, tire magnate Leonard K. Firestone, former CIA chief John A. McCone, aluminum magnate Edgar F. Kaiser Jr. and former Pan American head Najeeb Halaby, father-in-law of Jordan's King Hussein.

Today's Grove schedule, according to camp insiders, has included a lakeside talk by FBI Director William H. Webster, followed by Kissinger's talk, an organ concert and a stage performance. Saturday offers skeet shooting, a hike to the river, a band concert and a "low-jinks" review in which leading politicians and executives often sing and dance in drag.

Sunday, a Shultz aide said, Schmidt is scheduled to accompany Shultz back to his Stanford home, along with Lee and Kissinger, for more general talk.

A West German diplomat based in Washington said Schmidt "has a particular fondness for the United States." On vacation "he tries to get away from official duties and he finds it is almost impossible to do that in Europe. So he comes this distance for some freedom and he can also get in touch with people he does not know."

Thursday, for example, during a day in the San Francisco bay area, the chancellor ate breakfast with a group of leading West Coast editors, had lunch with experts on Germany at the University of California at Berkeley, dined with a leading Bay Area businessmen's council, met California Gov. Edmund G. (Jerry) Brown Jr., San Francisco Mayor Diane Feinstein and World Bank President A.W. Clausen and held a news conference.

The West German diplomat said: "It's not much of a vacation, to tell the truth."