Six years after declaring she was giving up live performances, Barbra Streisand returned to the stage yesterday to launch her first proper concert tour in well over a decade, and the biggest of her career. It will be only the second national tour by Streisand in the four decades since she became the toast of Broadway, launched a Grammy-winning recording career and won her first Oscar in the 1968 musical “Funny Girl.” Insisting she has conquered the stage fright that made her a virtual stranger to the concert circuit for years, Streisand, 64, says her comeback tour was sparked mostly by her desire to raise money for her favorite charities. The money will be distributed through her own philanthropic foundation. “That’s the main reason I’m going back on the road now,” she told Oprah Winfrey’s O magazine. According to one source close to the performer, Streisand plans to give around $10 million in proceeds from her 20-date, 16-city tour to such causes as environmental research, education and health issues. Last month, she announced that former President Bill Clinton’s “Climate Change Initiative” would be the first recipient, pledging a donation of $1 million.