"Happy Birthday to You" is up for sale, but the rights to one of the most popular tunes in the world are not going for a song.

The familiar four-line birthday song and the other tunes in the Birch Tree Group Ltd. catalog could command a price that has been estimated as high as $12 million, a Birch Tree executive said.The company's music library was put up for sale by David Sengstack, 66, a Princeton resident whose father purchased the rights to "Happy Birthday" years ago.

"We are a small educational company," said Kate Chen, publishing administrator for Birch Tree and a spokeswoman for company owner Sengstack.

"Managing `Happy Birthday to You' is a massive job," she said. "We don't want to operate on that scale. We want to concentrate on the company's early childhood music education concerns."

The Guinness Book of World Records lists "Happy Birthday" as one of the three most popular songs in the English language, along with "Auld Lang Syne" and "For He's a Jolly Good Fellow."

The song will become part of the public domain in 2010, when its 75-year copyright expires. Until that time, however, its owner can expect to continue collecting about $1 million a year in royalties, Chen said.

But keeping track of commercial uses of "Happy Birthday" and collecting the royalties is a time-consuming undertaking, since many people use it without realizing it is protected by copyright, Chen said.

"If you suddenly become aware that it's copyrighted, you will see it constantly on TV, in sitcoms," she said. "Movies use it all the time. There are musical greeting cards and music boxes. . . . We try to keep abreast of all that."

Parents needn't worry, however, that they'll be stuck with a royalty bill after their toddler's birthday party, Chen said.

"That falls under the question of whether it really is a `public performance,' " she said.

"Happy Birthday" was written by sisters Patty Smith Hill and Mildred J. Hill, two kindergarten and Sunday school teachers in Louisville, Ky.

In 1893, the sisters wrote a book, "Song Stories for the Sunday School," that contained a composition called "Good Morning to All," which had the melody of "Happy Birthday." Its lyrics were, "Good morning to you, good morning to you, good morning dear children, good morning to all."

The sisters later added the birthday words and the song has since been translated into languagues including Spanish, Dutch, Italian, Swedish, Malaysian and Ewe, an African language.

The Sengstack family obtained the song when New York accountant John F. Sengstack, David's father, purchased Clayton F. Summy Co., a Chicago sheet-music retailer that published the Hill sisters' work.

The song was copyrighted in 1935, protecting it for 75 years.

Some peculiar situations have arisen as a result of an effort to enforce the copyright of a song as popular as "Happy Birthday."

By law, any public performance for profit or mechanical reproduction should require a fee.

Summy sued Postal Telegraph in the 1940s when the song was used in singing telegrams. The lawsuit was dropped when company lawyers were stymied by the argument that even though the song was used for profit, it was not sung in public.