Every time somebody walks in the door of the Holocaust Memorial Museum, it costs American taxpayers $15.85.

That's 2 million visitors a year, and $31.7 million out of the public Treasury.It's much the same for all 16 museums of the Smithsonian Institution, which does not include the Holocaust museum, and for the National Zoo, which it also operates. Some 28 million people visit these sites annually - and pay nothing.

The operating cost passed on to taxpayers in this year alone: $371 million. It's a free pass worth $13.25 on average for each and every Smithsonian guest.

Even foreigners get in free. It costs Americans almost $52 million to pay their way. Yet Americans are charged to enter the finest museums in Europe.

Why the disparity? Why should Americans who don't come to Washington, D.C., and see these facilities help pay for tourists who do? And how does a favorite public place become a public burden?

The Holocaust Museum is a curious case in point.

Twenty years ago when it was proposed, the suggestion was for the government to donate the land and for private money to build it. It was reported that up to $60 million would be raised privately for an endowment fund to maintain it "in perpetuity." There was never mention, at first, of public funds being used except as "seed money" to get the museum started and then perhaps in a "challenge grant" to be matched in the private sector but just during the first three years.

Elie Wiesel, chairman of the council set up to raise private funds for the museum, said he hoped that ultimately, "We don't need the taxpayers' money."

In 1978 it was then-President Jimmy Carter saying he was setting up a commission to examine ways to get funds "for creation and maintenance of the memorial through contributions by the American people."

In 1983 it was then-President Ronald Reagan telling a gathering of American Jewish holocaust survivors that the nation was moving ahead to build a memorial "and it is being financed, as is this gathering, by voluntary contributions by Jews and gentiles, by citizens from every walk of life . . ."

Most of the cost of running the museum was through "voluntary contributions," as it turned out, in the sense that you volunteer your taxes to the Treasury.

By the time the Holocaust Museum opened, April 22, 1993, Congress was appropriating $18.3 million for its first year of operations. That cost has escalated every year since, to the point that today the public pays 60 percent of costs and private benefactors pay 40 percent. That's nearly $32 million from taxpayers, just under $17 million in private funds.

How did that happen?

"It seems that once a federal commitment is made, even to provide just a building site, requests for government money become inevitable," observes Pete Sepp of the National Taxpayers Union, a citizen watchdog group.

"This phenomenon occurs not just with museums but with federal office buildings, with such things as mass transit projects. Once the federal government nose is brought into the tent, the rest of the camel tends to follow."

There is no credible voice in Washington that is critical now of the Holocaust Museum's existence. It is stunning, in architecture, in spirit.

Visitors see photographs of the faces and emaciated bodies of genocide's victims and actual uniforms they wore, pass through a cattle car in which some rode to their deaths, watch films of uniformed Nazi murderers spewing hatred of Poles, Gypsies, Jews, gays. The museum is like a temple to the memory of the dead, a profound testimonial to human inhumanity. A shocked hush settles upon the people inside.

Nor does anyone seriously suggest giving up public ownership of any of the Smithsonian's museums - which also started out 150 years ago as a private endowment, the collection of a wealthy English scientist, James Smithson.

Seventy percent of the Smithsonian's operating budget is paid by taxpayers, yet the institution feels strongly that it should charge no entrance fees.

"We want to be as inclusive as possible," says communications director David Umansky. "The Smithsonians are the nation's museums. The 140 million-plus objects in our collections are held in trust for the American people."

Umansky says its different from going to the Field Museum in Chicago, for example, and coming to the Mall and being faced with six or seven Smithsonian museums.

"How do you charge for that in a way that doesn't restrict Americans access to their own museums," he asks. Even so, Umansky says the Smithsonian is studying how to get more voluntary contributions and has collection boxes at several museums now in pilot projects.

Meantime, however, some voices from the political right are asking why such attractions must weigh so heavily on taxpayers.

The Smithsonian's Air and Space Museum is now the most visited museum in all the world. Eight million people come yearly to see the moon rock, the Wright brothers' airplane, astronaut John Glenn's Mercury space capsule, Charles Lindbergh's Spirit of St. Louis.

Does any place so popular have to give it away?

At the conservative Heritage Foundation, analyst Scott Hodge proposes cutting federal contributions and requiring each such facility to cover half of operating costs with entrance fees.

Hodge points out that most public and private museums throughout the world charge fees or at least post signs for recommended contributions.

"It costs eight bucks to get into Mount Vernon, George Washington's boyhood home," Hodge notes. "The Hearst Castle in California charges $14 for a daytime tour, $25 for evening. New York's Museum of Modern Art sets a fee of $8. The Chicago Art Museum asks for donations of a specified amount, $6.50. England's Buckingham Palace charges visitors the equivalent of nearly $8. Spain's Prado Art Museum charges adults roughly $4 - though this charge applies only to foreign tourists."

Yet an estimated 14 percent of the visits to all the Smithsonian's facilities are by foreign tourists who enter free. That's 3.9 million of them - and $51.9 million out of American pockets.

"I think many foreigners are shocked at not having to pay anything," says Hodge.

Fee-charging is not embraced by all the groups that watchdog federal spending.

Gary Ruskin of Congressional Accountability Project says, "We like public subsidies of museums. We think it's important for Americans to know history and our democratic traditions. If you charge fees you cut down on the number of people who attend. A significant benefit accrues to the public for having a lot of people visit these museums."

Hodge acknowledges there is no political groundswell of support for his position: "It is really stepping on sacred territory and making yourself a target."