The red swimsuit that helped make Charlie's Angels actress Farrah Fawcett a 1970s icon became part of the Smithsonian museum's collection today on what would have been her 64th birthday.

Fawcett's long-time companion, Ryan O'Neal, presented the swimsuit and other items to the Smithsonian's National Museum of American History in Washington.

O'Neal said Fawcett, who died in 2009 after battling cancer for several years, always intended to give the swimsuit to the museum.

"They asked her years ago for the bathing suit," he said. "So it was always in her plan."

Fawcett wore the swimming costume for a photoshoot shortly before her debut on Charlie's Angels in 1976.

The resulting poster sold millions of copies and became the best- selling poster of all time, according to Smithsonian curator Dwight Bowers.

Mr Bowers compared the poster to Second World War pin-ups of Betty Grable and Rita Hayworth, saying it became a symbol of the 1970s era.

Though fans know the bathing suit as red, it is actually a burnt orange colour, possibly due to fading. Before it was donated to the museum, Fawcett framed it herself, and it was stored at a Los Angeles warehouse, O'Neal said.

Nels Van Patten, Fawcett's friend and tennis coach who was with her during the bathing suit shoot, said today that she did her own hair and make-up for the pictures and did not have a mirror. She also squeezed a lemon in her hair to get natural highlights, he said.

Also donated to the Smithsonian were Fawcett's book of scripts for the first season of Charlie's Angels, a 1977 Farrah Fawcett doll and a Farrah's Glamour Centre styling kit for creating her signature hairdo. The items will be part of the museum's popular culture history collection and will go on display this summer.

Fawcett's friends and family were at the museum today for the donation, including her son with O'Neal, Redmond O'Neal, and O'Neal's daughter, Tatum O'Neal.

Ryan O'Neal, who became choked up during the ceremony, said later that he feels Fawcett's presence every day.

"I'm still having trouble with losing her," he said.