Wangari Maathai, a Kenyan activist who founded an Africa-wide movement that empowered women, confronted corrupt officials and planted millions of trees in ravaged forestland, will receive the Nobel Peace Prize for 2004, the Nobel Committee announced Friday in Oslo.

Maathai, the first African woman to win the prize, is known as "Kenya's Green Militant." She has championed the environment for more than 30 years on a continent where many people live close to nature but find it under increasing pressure from development, pollution and war.

"We have added a new dimension to the concept of peace," said Ole Danbolt Mjoes, head of the Nobel Committee, which makes its decisions in secrecy. "We have emphasized the environment, democracy building and human rights, and especially women's rights."

An American-educated biologist, Maathai founded the Green Belt Movement in 1977, when she planted nine tree seeds in the yard of her house. In ensuing years, she and her movement succeeded in persuading women across Africa to do the same to fight the deforestation that is afflicting much of the continent. Trees help farmers by soaking up rain and preserving nutrient-rich topsoil; they also are a crucial habitat for wildlife.

Her group worked closely with village women, whose traditional duties include collecting firewood. By the millions, they were won over to the idea that planting trees and protecting the environment in other ways would help farming and long-term development of their communities and ensure a supply of wood.

Over almost three decades, the movement has brought about the planting of 30 million trees and given jobs to nearly 10,000 women who plant and sell seedlings to make a living. It was one of Africa's first female activist groups and has become a force in community affairs on a wide variety of issues.

"I feel so very excited, and I am very happy and very appreciative of all those who walked the road with me," Maathai, 64, said in a telephone interview. "Many wars we witness around the world are over natural resources. Without a properly managed environment, all of our lives are threatened."

Daniel arap Moi, who ruled Kenya as president for two decades, once called Maathai a "mad woman," and "a threat to the order and security of the country" for her tireless agitation to preserve forests. Moi's party lost a presidential election in 2002; Maathai was elected to parliament that year and is now assistant environment minister.

Maathai said in the interview that she survived critics by having "the thick skin of an elephant."

The tall and velvet-voiced Maathai joins past laureates who include former president Jimmy Carter, U.N. Secretary General Kofi Annan, Mother Teresa, Nelson Mandela, the Dalai Lama and Martin Luther King Jr.

She will receive the award in Oslo on Dec. 10. But on Friday, she celebrated by removing her jewelry, kneeling in the dirt and planting seeds of a Kenyan tree known as the Nandi Flame on the grounds of the Outspan Hotel in Nyeri, her home area in the foothills of Mount Kenya.

President Mwai Kibaki hosted her at the Nairobi State House on Friday evening for a celebration. "Prof. Maathai has waged a sustained campaign to protect our environment," Kibaki said in a statement. "As Kenyans we must re-dedicate ourselves to the fight to conserve the environment as a gesture of appreciation of the prestigious award to one of our own."

Her efforts were not always cherished. In 1989, she led a one-woman charge in court against Moi's autocratic government, after he proposed building the tallest skyscraper in Africa and a six-story statue of himself in the only public green space in Kenya's gritty capital.

"She was threatened physically and was called a busybody in the press, yet she didn't flinch," said Mwalimu Mati, deputy directory of Transparency International, an anti-corruption group with offices in Nairobi. "It was like watching a lone, unknown voice stand up against the whole. She really deserves this, because she's converted a lot of us to understand why the environment is so important. Now she has the real moral authority to challenge people who are selfishly allocating themselves land."

She was famous at the time for saying publicly, "We can provide parks for rhino and elephants; why can't we provide open spaces for the people? Why are we creating environmental havoc in urban areas?"

A lawsuit she filed against the $200 million, Moi-backed project was dismissed. But by then, her protests had scared away investors.

In 1992, she and other women stripped naked in downtown Nairobi to protest police abuses. She said that in taking off their clothes, the women had "resorted to something they knew traditionally would act on the men. . . . They stripped to show their nakedness to their sons. It is a curse to see your mother naked."

On Jan. 8, 1999, she was whipped on the head and arrested by security forces allegedly hired by Moi to disperse Green Belt Movement members who were protesting the clearing of Karura Forest near Nairobi for a luxury housing development. She caught the nation's attention by insisting on signing her police report in blood from her head injury. The houses were never built.

She is also a rare African feminist, whose husband left her in a nasty public divorce. He won the settlement dispute on the basis that she was, by her own account, "too educated, too strong, too successful, too stubborn and too hard to control."

She has been a passionate fighter for women's rights, leading by example on a continent where women often live as second-class citizens, do most of the labor, but have the legal rights of children. Their rights to own property, for instance, are often limited.

Maathai grew up in a Kenyan village, the daughter of farmers. She excelled at the local school and applied repeatedly for scholarships to continue her education, eventually winning one to attend college in the United States. In 1964, she received a degree in biological sciences from Mount St. Scholastica College in Atchison, Kan. She received a master's degree two years later from the University of Pittsburgh and, in 1971, a PhD from the University of Nairobi. That made her the first woman in eastern and central Africa to earn a doctorate. She also became the first female professor at the University of Nairobi.

At times, she has generated jealousy among her peers.

"I have had the fortune of breaking a lot of records," Maathai said in a 1992 interview with The Washington Post. "First woman this. First woman that. And I think that created a lot of jealousy without me realizing. Sometimes we don't quite realize that not everybody's clapping when we're succeeding."

David Makali, director of Nairobi's Media Institute, said he hoped Maathai's newfound global fame would draw attention to a current land-grab controversy in Kenya. Top government officials, including Moi and another former president, Jomo Kenyatta, are accused of seizing public lands for their personal use and arranging the clearing of trees for fast profits.

The award "is fabulous news . . . for Kenya and Africa," Makali said. "This will increase the visibility of the country and our campaign to be better watchdogs over our country's land."

Last week, Maathai threatened to give up her seat in parliament to protest a plan to use forestland for small-scale farming. "I would rather give up my seat than see our forests destroyed," she said Friday.

She added that, prize or no prize, she would continue her fight, for the sake of young Africans.

"The generation that destroys the environment is usually not the generation that suffers," she said. "If they go into the forest, they will be digging their own graves and that of their children and grandchildren."

Wangari Maathai's Africa-wide movement empowers women through the planting of trees. American-educated biologist Wangari Maathai, 64, speaks on the telephone to well-wishers near Nyeri, her home in the foothills of Mount Kenya.