Elections provide a temporary guide to presidential popularity. It takes an auctioneer's gavel to measure lasting appeal.

Today and tomorrow, Guernsey's, the auction company that turned Mark McGwire's 70th-home-run baseball into a $3 million collectible, will test the market for presidents through a sale of their artifacts. Over both days at the New-York Historical Society and live on eBay.com, Guernsey's will offer mountains of memorabilia and a few rare treasures. Highlights of the 691 lots include two flags from John F. Kennedy's Oval Office and one enormous 1858 flag stitched for the second Lincoln-Douglas debate.

An intriguing selection of artists' studies for 20th-century presidential portraits includes work by Aaron Shikler, Elizabeth Shoumatoff, Ellen Emmet Rand, Samuel J. Woolf, Peter Hurd, Herbert Abrams, Robert Templeton and Everett Raymond Kinstler.

The catalogue also features a photographic archive by Robert Knudsen, a Navy photographer later assigned to the White House, whose camera recorded the workday and family life of presidents from Harry Truman through Richard Nixon.

Especially intriguing is the set of handprints made by Franklin and Eleanor Roosevelt, complete with analysis by their palm reader. A so-called "presidential pardon," which is not pictured, is said to have been a spoof of the Johnson administration by the incoming Nixonites. Six administrations' worth of White House menus were preserved by Sanford Fox, an aide to the social secretary's office. Like many other items in this sale, the cache is now being sold by heirs.

In this "as is" auction, the buyer accepts certain risks. Guernsey's and its consigners include a disclaimer of "any and all warranties" including accuracy of the catalogue and any statements concerning rarity, attribution, authorship, provenance and historical relevance. Some flags carry estimates in the hundreds of thousands of dollars, while keepsakes such as cuff links and Christmas cards are listed at a few hundred dollars.

"Everything has a value," says Harry Rubenstein, a curator of political history collections at the Smithsonian's National Museum of American History. The desire to preserve the ephemera of an administration shows "our fascination with the American presidency and how we want as a people to have a tangible piece of that aura."

Of dozens of items from the Kennedy years, a slim red hardcover volume of poems and drawings titled "Caroline Kennedy First Lady Dress-Up Book" vies for most poignant. A young Caroline smiles forth from the cover. Inside, cartoon-like images show Caroline dressed up as historic first ladies. The catalogue describes the author as Arlene Dalton, a friend of Jacqueline Kennedy's, who is said to have been closely involved. Guernsey's founder, former advertising executive Arlan Ettinger, believes the book, which was consigned by the printer, is one of four copies left from a test run of 20 that were to be introduced in late November 1963. The Smithsonian, which owns two copies, cannot vouch for provenance, but confirms the copyright is 1963.

A collection of 125 Time magazine cover paintings made between 1939 and 1956 by Ernest Hamlin Baker includes two presidents but is more noteworthy for chronicling Henry Luce's version of history via portraits, including those of Joseph Stalin, Nikita Khrushchev and William Randolph Hearst, as well as Marlon Brando and Bing Crosby. The paintings were consigned by a private collector and are offered as a single lot with a $300,000 minimum.

Ettinger has carved out a niche in the auction world by marketing to the broad public rather than to specialist collectors. His first auction 27 years ago, of discarded wooden carousel horses, created a folk-art market for languishing pieces of Americana. In May he banged the gavel at $850,000 for Jerry Garcia's Grateful Dead guitar. Ettinger declines to ponder the relative cachet of White House history and celebrity guitars.

"I'm just an auctioneer," he says, "not a philosopher."

Auctioneering can be tough enough. In 1998, Guernsey's previewed a major sale of Kennedy memorabilia, which sparked a lawsuit from the Kennedy children and led to the withdrawal and transfer of items to the National Archives and John F. Kennedy Library and Museum.

This time, he says, "the first call we made was to the White House -- the library, the archivist, and curators there -- to let them know. We are a business, but hopefully a caring one."

The Kennedy Oval Office flags were to have been part of that first sale. According to Ettinger, they were consigned by the University of Pittsburgh, which received them from the estate of Evelyn Lincoln, Kennedy's longtime secretary. Lincoln is said to have received them from Jacqueline Kennedy after her husband's assassination.

After pre-sale controversy over the propriety of the auction, whose lots were to include such items as longjohns and Jacqueline Kennedy's 1960 handwritten will, the university withdrew the flags. Last November, Ettinger went on the "Today" show and offered to sell the flags in a telephone auction. Noting a post-9/11 patriotic fervor, Ettinger told Katie Couric that he would consider bids exceeding $750,000. He says that a buyer emerged but the sale was never completed. Now as then, proceeds are intended to go to a university scholarship fund.

Oval Office flags are neither the best nor the brightest barometer of presidential appeal. Over four hours in March, Christie's New York auctioned Malcolm Forbes's fabled collection of U.S. historical documents, many of them presidential in nature, for more than $20 million. A second Forbes sale on Oct. 9 added $9.3 million to the total. Records were set for 16 presidents.

The Christie's offerings were the kind of scholarly documents that serious collectors compete for. In the March sale, an anonymous buyer paid more than $2 million for a 1939 letter from Albert Einstein to Franklin Roosevelt, which is said to have influenced the president to launch the Manhattan Project and develop the atomic bomb. A 12-page manuscript of Abraham Lincoln's last public address, which contained the president's first public appeal for voting rights for black Americans, sold for more than $3 million, almost double the record for an American historical document. Last month, a manuscript from George Washington's early military career sold for $834,500, while a letter on slavery by Thomas Jefferson went for $669,500.

On Dec. 19, Christie's will offer 125 lots of mostly presidential materials, including a rare copy of the Emancipation Proclamation signed by Abraham Lincoln. According to Chris Coover, Christie's senior specialist in the printed books and manuscripts department, the document is one of 15 to 20 such authorized signed copies, which were offered for sale for $10 each at the time.

At these levels, museums are mostly priced out of the market.

"Some of these things are extremely expensive and will go for possibly hundreds of thousands of dollars," says Rubenstein, who would be delighted to accept a gift of the historically significant Lincoln-Douglas debate flag, should the winning bidder decide the 6-by-11-foot banner deserves to be in a Washington museum.

But Coover says he is aware of a few institutions that are still working carefully to fill gaps in their collections. One he mentions by name is the Mount Vernon Ladies Association, which he describes as "active in the market" for good George Washington material. The Christie's sale will include a rare exchange of notes between George and Martha Washington. After the president's death she burned their personal correspondence, making any communication, even a postcript on another's letter, extremely valuable. And yes, the Mount Vernon Estate would be overjoyed to get this one as a gift.

Guernsey's trove includes a leather leg brace said to be from the collection of Grace Tully, FDR's White House secretary, which has a pre-sale estimate of $7,000. That's half the amount Guernsey's expects Roosevelt's opening-day baseball passes from 1944 will bring. As for such keepsakes as tie tacks and signing pens, Rubenstein suggests, "their value and their meaning is what people bring to them." For people seeking to own a piece of American history, "presidential material has a real pull."

Coover cautions that there are plenty of things floating around that reportedly were "used, held or owned" by a historical figure, and savvy collectors will be "extremely careful looking into the history and provenance of these items." That's one reason he favors signed documents. But even a bona fide signature bears scrutiny.

The Guernsey's catalogue presents a check as being signed by "President George Washington" and two others on Aug. 5, 1786. Washington, of course, did not become president of the new nation until 1789. A quick look in Mount Vernon's archives enabled Associate Director Linda Ayers to place the future Founding Father in Alexandria on that day, at a meeting of the Potomac Company.

Washington was the group's president.

A test-run copy of a book featuring young Caroline Kennedy that was to have been published in late November 1963.George Washington memorabilia up for auction include a 1855 French portrait woven in silk.A flag prepared for the second Lincoln-Douglas debate, left, is expected to fetch a high price; above, a leg brace used by Franklin Roosevelt.