The essence of the brief holiday President Reagan is taking on his mountaintop ranch 30 miles northwest of here was summed up this week in a press aide's reply to a California reporter who asked what events were on the schedule.

"There are two events," the aide said. "Arrival and departure."

And that's the way it is at Rancho del Cielo, where the president of the United States spent the morning riding a horse called "Little Man" and the afternoon chopping firewood, which will be used next winter to warm his otherwise unheated Spanish-style ranch house.

"We are not going to have a western White House in the sense that we're going to have a major government compound there," said White House counselor Edwin Meese III on the presidential flight from Andrews Air Force Base to California last Thursday.

In fact, there is not even a minor government compound in the works at the 688-acre ranch, which Reagan and his wife Nancy bought in 1974 for $526,000. Secret Service agents sleep in a mobile home, as do Reagan's physician and military aide. Lee Clearwater, the permanent caretaker on the ranch, sleeps in a larger mobile home nearby. The other Reagan staff, and the platform of communications and transportation aides who accompany any president wherever he goes, take rooms at the same Santa Barbara beachfront hotel where the traveling press corps is quartered.

The Reagans are so careful of their privacy that they even vetoed the usual press "photo opportunity," which had been requested by some of the television networks.

"The president's here for rest and relaxation, and he's going to get it," an aide said in rejecting the request.

The ranch on which the Reagans are enjoyingf their seclusion is a rugged and remote brush-covered retreat whose status as "agriculture preserve" land keeps the taxes bearable.

"Agricultural preserve" is a device used in California and other states to protect desirable land from being turned into subdivisions. In California it has support from conservative ranchers and growers because it keeps taxes low and from liberal environmentalist groups because it helps preserve some of the state's most attractive landscapes. Nearly half a million acres is zoned agricultural preserve in Santa Barbara County, and Rancho del Cielo enjoyed this designation three years before the Reagans bought it.

Because of the agricultural preserve zoning, the Reagans paid $1,148 in property taxes this year. They graze 22 head of cattle on the ranch to qualify.

No one knows what the Reagan ranch would bring on the market, but a $2 million estimate which has been used in the past apparently is very conservative. Reagan's nearest neighbor, Stuart Eckert, recently sold 105 adjoining acres for at least $1 million.

The Reagans have assured this preservation-conscious community that they don't desire development, which would be difficult in any event because of the lack of water and the high summer fire hazard at Rancho del Cielo.

The ranch is accessible only by helicopter or by motor vehicle over a twisting 6.5-mile road that runs up into the Santa Ynez Mountains from Refugio State Beach. The road, heavily patrolled, is full of potholes from winter rains. Helicopter flights also could become a problem later in the year because of fog.

The Reagans are trying to sell their home in Pacific Palisades, and the ranch already has been designated their "principal nongovernmental residence."

Though Reagan much prefers the ranch to Pacific Palisades, there is a price for the inaccessibility and privacy that he is attempting to retain. It comes in the unpublished cost of establishing a sophisticated security system and miles of expensive communications lines on Rancho del Cielo, where at late as last summer hikers sometimes invaded the Reagan property without even knowing where they were.

Some of the security problem is being solved by the means of transportation Reagan prefers over all others -- horseback. At a nearby stable, Secret Service agents are taking riding lessons because a number of them reportedly have been unable to keep up with the president on his morning rides.

On this trip, at least, administration aides have not tried to pretend that Reagan is doing much serious work. The president was given a written national security briefing this morning and a stack of other papers. Otherwise, he and Nancy had the day to themselves.

The only sensitivity shown by the Reagan staff was about a question that has haunted presidents whenever they take vacations -- the cost of leaving Washington with the legions of people who move with a chief executive. It costs $110,000 to fly Air Force One and its backup plane on a round trip across the continent. Total costs, which doubtless include much of the communications equipment, have been estimated at as high as $250,000.

The president and his advisers believe the costs are justified to give him rest and perspective. Those who have known Reagan over the years point out that he always has required periodic "battery recharging."

His work habits were developed in the movie business where several weeks of film-making often were followed by several weeks of doing nothing. This is still Reagan's preferred style, and he proposes to take time off whenever he can even as president of the United States. As much of that time as possible will be spent at Rancho del Cielo.