Nobody, but nobody, is allowed inside Camp David who isn't a president, a first lady, a very highly placed foreign visitor, or a first kid, dog, friend or aide. For that matter, the closest anybody can get to the 143-acre presidential retreat in Maryland's Catoctin Mountains is a road sign that obliquely proclaims "Camp 3." Only the anointed are cleared to drive beyond it to where, a couple of hundred yards on up the road, another sign identifies the hideaway as "Camp David."

Imagine, then, the excitement of Maryland Public Television producer-director Lori Evans to learn after months of pulling together the TV special "Camp David" (Channel 26, 10 p.m. Friday) that the White House had finally reversed itself. Evans & Co. would be permitted to film standups of the film's narrator, broadcast journalist Ann Compton, in front of the "Camp David" sign after all.

"I was so thrilled," Evans recalls. "I thought at least we'd be by the gatehouse and that we had been extended special privileges."

But no such luck. In a sleight of hand not unlike the old shell game, the White House merely had switched the signs. Instead of "Camp 3," there in its place stood "Camp David."

Vladimir Feltsman, the Soviet pianist who made his American concert debut Sunday at the White House, credited efforts by President Reagan and Secretary of State George Shultz with helping him win an exit visa from the Soviet Union after an eight-year wait.

"President Reagan asked for me twice at summits {with Soviet leader Mikhail Gorbachev} and Shultz also asked," Feltsman told reporters in a brief press conference arranged by the White House.

Dramatically positioned so that the mansion's North Portico was in the background, Feltsman said he and his wife Anna hope to become American citizens eventually. Asked if he planned to help other Soviet citizens, including artists, who are trying to leave the Soviet Union, Feltsman looked a little puzzled.

"How can I do it?" he asked. "We have a number of friends who are refuseniks. We'll remember them."

Shultz was among the concert guests, as were USIA Director Charles Z. Wick, national security adviser Frank Carlucci and former U.S. ambassador to the Soviet Union Arthur Hartman and about 200 others from the arts, the media and New York and Washington society.

Soviet Ambassador Yuriy V. Dubinin was not invited because "basically, it was a cultural event -- a musical evening, not a political evening," said Elaine Crispen, Nancy Reagan's press secretary.

Nobody knows how the Reagans' Santa Barbara ranch stacks up against Mikhail Gorbachev's personal dacha, but one thing that might impress him on his American odyssey is California's colossal farm industry.

Publicly the president continues to say he doesn't want the Soviets to get the idea that their American hosts are "staging" Gorbachev's visit. But besides his ranch, where he reportedly would like to entertain Gorbachev at lunch or dinner, President Reagan is said to be hankering to show Gorbachev what the Golden State's agribusiness looks like from the air.

"Just flying over the San Joaquin Valley is enough to drop anybody's jaw," Maureen Reagan, first daughter and cochairman of the Republican National Committee, said last week.

Maureen, who has no official role in the visit, said she'd like Gorbachev to see "what the president wants him to see, and that is how people live in this country -- the blue-collar workers who go home to their own homes at night, which is 180 degrees away from the way they live in the Soviet Union.

"I don't know that it's going to make Mr. Gorbachev change his philosophy of life, but I think it would be something interesting for him to see," said Maureen, who also says she'd put a supermarket and a used-car lot on the "must see" list for the Gorbachevs.

She was less enthusiastic about the idea of visits to Disneyland or a Hollywood movie studio. "That's really more of an entertainment," she said as she and husband Dennis Revell were about to embark on a 12-day trip to the People's Republic of China.

Invited by the P.R.C. in her capacity as U.S. representative to the U.N. Commission on the Status of Women, Maureen Reagan will meet with China's women leaders in Beijing, Xian, Shanghai and Canton.

West German Ambassador Guenther van Well and his wife Carolyn gave an informal supper dance Friday night for the unsung heroes and heroines of Capitol Hill -- congressional staffers.

"We wouldn't think of trying to interfere in the domestic affairs of the United States," van Well wryly assured his 100 or so guests, whom he wined and dined with vintage Mosels and Rheingaus and prime beef tenderloin. The pie`ce de re'sistance was the First Army Corps Band flown from Germany to Washington especially to play for dancing.

For van Well, the party was one of his last as ambassador. He turns 65 this week, the mandatory retirement age for German government employes. The van Wells will leave Washington after a farewell reception Oct. 23 and plan to divide their time between Connecticut and Bad Godesberg, West Germany, where they have homes.

About a half-dozen luncheons, dinners and receptions are in the works this week for Melina Mercouri -- not because she's one of Greece's best known contemporary attractions but because she's its minister of culture.

As such, she's in town to talk about some coming attractions: antique Greek treasures that will go on display in January at the National Gallery of Art, and cultural exchanges that she hopes to work out with Assistant Secretary of State Rozanne Ridgway and USIA Director Wick.

The 67-piece exhibition from the 9th to 5th centuries B.C. is entitled "The Human Figure in Early Greek Art." Most of the works will be traveling abroad for the first time.

Among Mercouri's hosts: Wick, J. Carter Brown, Greek Ambassador George D. Papoulias and Sen. Larry Pressler (R-S.D.). She'll open Greek Month in Canada and sign a draft cultural agreement before returning home.

The French, two years away from the bicentennial marking their own revolution, have drafted an American committee to help them celebrate on this side of the Atlantic.

Last week, Edgar Faure, a former prime minister who heads the French Committee for the Celebration of the French Revolution and the Declaration of the Rights of Man and the Citizen, met at the French Embassy with a group of 36 Francophiles presided over by former senator Charles McC. Mathias Jr. of Maryland.

Before it was over, former U.S. ambassador to France Arthur Hartman and arts patron Leonard Silverstein agreed to serve as secretary and treasurer, respectively, of a foundation to advise, coordinate and raise money for festivities in this country.

Among others at a reception and dinner hosted by French Ambassador Emmanuel de Margerie were Walter Annenberg, David Rockefeller, Kay Shouse, Jessye Norman, Sargent Shriver, James Billington, Robert McC. Adams, Warren Burger, the Rev. Benjamin Hooks and Joe M. Rodgers, current U.S. ambassador to France.

White House spokesman Marlin Fitzwater began his long-promised physical fitness program last week. Fitzwater said the program involves a "mostly salads" diet and riding an exercise bicycle in an Old Executive Office Building workout room for "five minutes or one mile, whichever comes first."

"It's kind of like the Chrysler plan -- a little bit at a time.