By Patrick Worsnip

UNITED NATIONS (Reuters) - Sales of a bracelet will go towards a U.N. fund to combat violence against women under a plan announced on Tuesday by the United Nations, the Avon cosmetics company and movie star Reese Witherspoon.

Avon Products Inc., the world's biggest direct seller of cosmetics, has pledged to match the first $500,000 in sales of the bracelet to benefit the fund aimed at ending a problem activists say affects one woman in three worldwide.

Witherspoon showed off the "women's empowerment bracelet" at a U.N. news conference, saying its clasp in the shape of the infinity symbol -- a horizontal figure of eight -- represented "a future without limitations for all women."

Joanne Sandler, head of the U.N. women's agency UNIFEM, said the public-private partnership -- a model favored by Secretary-General Ban Ki-moon -- would bring "badly needed resources" to the U.N. Trust Fund to End Violence against Women.

Describing violence against women as a "hidden pandemic," Sandler told the news conference that in the United States alone lost productivity and earnings due to violence by domestic partners cost almost $1.8 billion a year.

The bracelets will cost $3 and be sold by Avon's network of 5.4 million sales representatives around the world, primarily women who run home-based businesses.

Avon chief executive Andrea Jung said the money raised would help UNIFEM improve implementation around the world of laws and policies dealing with violence against women.

Past efforts have included grants to help India's legal system implement a new domestic violence law and to assist the Rwandan government to establish a special police unit to investigate cases of violence.

Witherspoon, 31, who won a best actress Oscar playing country singer June Carter in "Walk the Line" but is a producer of her latest movie "Penelope," said she hoped to "use my recognizability for a cause that I think is very important."

Asked about violence against women portrayed in Hollywood, she said her response was to "really depict women that I see socially, women who are strong and accomplished and self-respecting."

She left it to Jung and Sandler to answer a reporter who asked whether Western cosmetics and the way Witherspoon herself was dressed -- she was wearing a short-sleeved, v-necked black dress -- might alienate people in conservative countries.

"People like Reese Witherspoon have such a powerful message, such a powerful resonance with so many women and men that actually one kind of transcends, I think, that issue," Sandler said.

(Editing by Cynthia Osterman)