LOS ANGELES (Reuters) - She was among the most photographed celebrities of her day, and he is among the top pop stars of his. But whose pictures are worth more -- Marilyn Monroe or Justin Bieber?

Memorabilia collectors and fans of the two stars will soon find out in a four-day, December auction of Hollywood memorabilia, called Icons and Idols, from Julien's Auctions.

The images of Bieber behind the scenes of his music video for One Less Lonely Girl and Monroe, which vary from items when she was an unknown to those when she was star, are just a few of the 1600 items from film, music and sports figures expected to go under the hammer in a sale that could fetch $2 million to $4 million, auctioneer Darren Julien estimated.

The 14 Polaroid photographs of Bieber, 17, were taken by a crew member on the video set, and are estimated to sell for $1,200. But when his legion of young Beliebers catch wind of the sale, that price could skyrocket to somewhere up around $6,000, Julien believes.

He is highly collectible, and these kind of photographs rarely go on sale. I don't think Justin ever intended them to go on sale, said Julien.

Yet, unlike a known commodity such as Monroe, star of films including Some Like It Hot and The Seven Year Itch, Bieber still might flame out as a pop idol.

He's young and in some ways he still has to prove himself, but he's got the talent to be like John Lennon or Paul McCartney. He's got that potential, and he can be at that level of collectibility, said Julien.

The Monroe items range from early pictures of her as a 19-year-old and a never before sold letter, expected to fetch $30,000 to $50,000, she sent to her mother while still known as Norma Jeane and married to Jimmie Dougherty in which she talks of her future hopes.

Also up for sale is an image taken by Cecil Beaton after Monroe became a movie star in which the actress is reclining with a rose. The pictures were put in a Cartier triptych frame and said to be her favorite images of herself. It's estimated sale price is $80,000-$100,000.

With prices like that, it's very likely the Bieber photos will fall far short of Monroe's, but his fans can take heart in the title of his own song, Never Say Never.

Personal items of late singer Michael Jackson also will be up for sale, including rare candid photographs of the King of Pop with actress Elizabeth Taylor and an oil painting of Disney characters Mickey Mouse and Pluto, painted by the singer.

Other items on sale include garments from Lady Gaga, Cher and the Beatles, as well as a signed guitar from U2's Bono.

Sports fans also have their share of historic memorabilia to bid on, including basketball player Michael Jordan's 1984 John Wooden Award and an original stadium locker attributed to famed Yankees baseball player Lou Gehrig.

More information can be found at www.juliensauctions.com

(Editing by Bob Tourtellotte)