(Adds reaction from former President Clinton, Neil Diamond, paragraphs 12-13; details on other honors, fifth paragraph from end)
By Diane Bartz
Jan 28 (Reuters) - Pete Seeger, who helped create the modern American folk music movement, co-wrote enduring songs like "If I Had a Hammer" and became a leading voice for social justice, died on Monday at the age of 94.
He was hailed in social and traditional media as a "hero," "America's conscience" and "a man of the people."
Seeger died of natural causes at New York-Presbyterian Hospital, his record company, Appleseed Recordings, said.
Seeger was well known for his liberal politics. He protested U.S. wars from Vietnam to Iraq, participated in the civil rights movement, supported organized labor and helped found an environmental group that played a key role in cleaning up the polluted Hudson River.
In 1961, he was sentenced to prison for refusing to testify to Congress about his time in the Communist Party.
Nearly a half-century later, Seeger performed at a January 2009 concert marking the inauguration of President Barack Obama.
"He believed in the power of community - to stand up for what's right, speak out against what's wrong, and move this country closer to the America he knew we could be," Obama said in a statement. "For reminding us where we come from and showing us where we need to go, we will always be grateful to Pete Seeger."
In May 2009, Seeger celebrated his 90th birthday with a concert in New York's Madison Square Garden that drew 15,000 spectators and performers, including Bruce Springsteen, John Mellencamp, Emmylou Harris, Arlo Guthrie, Joan Baez and Kris Kristofferson. Proceeds went to Seeger's environmental group, Hudson River Sloop Clearwater.
"Like a ripple that keeps going out from a pond, Mr. Seeger's music will keep going out all over the world spreading the message of non-violence and peace and justice and equality for all," Jim Musselman of Appleseed Recordings said in a statement.
Documentary filmmaker Michael Moore recalled on Twitter how in October 2011 he was on a street in New York and saw Seeger leading an impromptu protest march.
"Pete Seeger. What can I say. He said it and sang it and lived it all. Our paths crossed many times, and I am the better for it," Moore tweeted.
Former President Bill Clinton, who presented Seeger with the National Medal of the Arts in 1994, in a tweet praised the performer's great heart and commitment to social justice.
Singer Neil Diamond described Seeger as a messenger of universal love and peace. "He was my first inspiration to write songs and share music in my own way. God bless," Diamond tweeted.
Seeger and another folk music icon, Woody Guthrie, started the Almanac Singers in the early 1940s. In 1949, Seeger helped found another key folk group, the Weavers. Those groups opened the way for Bob Dylan and another generation of folk music singer/songwriters in the 1960s and '70s.
The Weavers had a No. 1 hit with a version of blues and folk musician Lead Belly's "Good Night, Irene" and by 1952 the group had sold more than 4 million records. The members soon drifted apart, however, after being blacklisted for links to the Communist Party.
Seeger and Lee Hays wrote "If I Had a Hammer" for the Weavers, along with the hit "So Long, It's Been Good to Know You."
Seeger also wrote the modern classic "Turn! Turn! Turn!" with lyrics from the Bible's Ecclesiastes and "Where Have All the Flowers Gone" with Joe Hickerson. But he was modest about his songwriting.
"Hardly any of my songs have been written entirely by me," he said in an interview. "I swiped things here and there and wrote new verses" to old tunes.
'LOST MY HEART TO THE BANJO'
Seeger, born on May 3, 1919 in Patterson, New York, was the son of two teachers at the famed Juilliard School of Music - his father an ethnomusicologist and his mother a violinist.
He became interested in folk music through his father, who directed family friend Aaron Copland to the music of West Virginia coal miners, resulting in the classical music works "Appalachian Spring" and "Fanfare for the Common Man."
Another of his father's friends was folk archivist Alan Lomax, who hired the younger Seeger to classify recordings at the Library of Congress in Washington.
A key moment in Seeger's life was attending a mountain dance festival in North Carolina with his father.
"I lost my heart to the banjo," he said later. "It was an exciting sound and there was a kind of honesty in country music that I didn't find in pop music."
In 1938, Seeger dropped out of Harvard University and took his banjo on the road. During his travels, he met Guthrie at a benefit concert for California migrant farm workers.
Seeger's career was derailed in 1951 when a book listed the Weavers as Communists. During the next year, the group's record company dropped them and they were refused radio, television and concert appearances.
Seeger had been a Communist Party member but left around 1950. Still, he refused to answer questions from the U.S. House of Representatives Un-American Activities Committee in 1955, was prosecuted and sentenced to a year in jail in 1961.
The conviction was overturned on appeal, but Seeger's career did not begin to recover until 1967 when the Smothers Brothers, a folk and comedy duo, invited him to appear on their variety TV show.
Seeger spent the next two decades performing on college campuses, at folk festivals and political rallies.
The singer won two Grammy awards for best traditional folk albums for "Pete" and "At 89," and another for best musical album for children for "Tomorrow's Children." He also received a Lifetime Achievement Grammy in 1993.
In 2007, Springsteen won the best traditional folk Grammy for "We Shall Overcome - the Seeger Sessions," a collection of songs popularized by Seeger.
In addition to the National Medal of the Arts and the Grammys, Seeger was a 1994 recipient of the Kennedy Center Honors, an annual award given to a select group for contributions to American culture.
Seeger lived in Beacon, New York, along the Hudson River north of New York City, and the river's health was a cause that was literally close to home.
In the mid-1960s, Clearwater, the group he helped found, built a sailing sloop like those from the 18th and 19th centuries. The vessel, also named Clearwater, traveled up and down the Hudson to promote the group's cleanup campaign and to provide environmental education.
Seeger also wrote children's books.
His wife, Toshi, whom he married in 1941, died in 2013. They had three children. (Additional reporting by Mary Milliken and Patricia Reaney; Editing by Bill Trott, Jeremy Gaunt and Jonathan Oatis)