LONDON – A Shakespeare First Folio that has been hidden in one of Britain’s most esoteric libraries for almost 300 years is to go under the hammer with the possibility of threatening the world record price for any book sold at auction.

Sotheby’s said yesterday that the 950-page volume, on which it has put $4.4 million to $6.1 million estimate, is the best example of a First Folio edition to reach the market in 60 years.To whip up interest from international buyers, it will take the book on a world tour before the sale in London in July.

Only 18 of Shakespeare’s plays were published in his lifetime and it was not until 1623, seven years after his death, that the so-called complete works – a total of 36 plays – appeared in what is now known as the First Folio.

Some 750 copies were printed – and sold for a guinea – but today only a third survive.

Some are in poor condition, others have pages missing, pages replaced with later facsimiles, or have been cannibalized with leaves from other copies.

Sotheby’s experts said yesterday that they were “quietly confident” that the volume can beat the record auction price for a First Folio, $5.6 million set by Christie’s in New York in 2001. Also in its sights could be the record price for any book – $7.6 million for a copy of “Audubon’s Birds of America,” set in New York in 2000.

Sotheby’s edition also has an extraordinary history,and appears never to have left London. It belongs to Dr. Williams’s Library, the country’s pre-eminent collection of puritan, Protestant non-conformist, and dissenting books and manuscripts, founded in the early 18th century from a bequest of books, including the First Folio and a $87,000 endowment by Dr. Daniel Williams, a prominent 17th-century dissenting minister.

The library, now in Gordon Square in central London, has 300,000 titles but only 1,000 members and says that it receives no public funding and needs to sell its most valuable asset to secure its future. Insuring the First Folio accounts for one third of its annual premiums.

Dr. David Wykes, the director of the library, said that the institution was “sorry” to sell the volume but it had watched its valuation grow from $30,000 in the 1960s to $1 million 15 years ago with a mixture of concern and amazement.

A copy of the First Folio might not seem an obvious choice of reading matter for a fire-and-brimstone Nonconformist – after all, Cromwell’s Puritans banned all stage performances from 1642 until the Restoration.

Dr. Wykes said Dr. Williams had a strong interest in literature as well as religion and his bequest had included plays by Ben Jonson and John Dryden.

It is believed that Dr. Williams bought the First Folio and a complete library from a fellow Nonconformist minister, Dr. William Bates, for pounds 500.

The volume is in its original mid-17th century binding and has the extra attraction of numerous notations. An unknown scholar, probably in the mid-17th century, has underscored or marked hundreds of lines. His work appears to have been erratic.

He made 380 markings by “Henry VIII,” several dozen by each of the other plays, but not one on “The Merry Wives of Windsor.”

Another 17th-century hand, possibly that of a naughty child, has written something quite different on one page.

The single sentence reads: “But I desire the readers mouth to kis the wrighteres arse.”

Dr. Roe said: “This does not devalue the volume.It adds to it. It demonstrates that it is a good, honest, working book.”