OSLO, Oct. 8 — Wangari Maathai, a Kenyan woman who started an environmental movement that has planted 30 million trees in Africa and who has campaigned for women's rights and greater democracy in her home country, today won the 2004 Nobel Peace Prize.

She is the first African woman to win the peace prize since it was first awarded in 1901. Last year, the prize was awarded to another woman, Shirin Ebadi, in recognition of her work promoting the rights of women and children as a lawyer in Iran .

Announcing the award here, the Nobel committee chairman, Ole Danbolt Mjoes, said Ms. Maathai "represents an example and a source of inspiration for everyone in Africa fighting for sustainable development, democracy and peace."

With the award, the Nobel committee expanded the traditional boundaries of the peace prize that were laid out in 1896 in the will of Alfred Nobel, the Swedish inventor of dynamite. He decreed that it should go "to the person who shall have done the most or the best work for fraternity between the nations, for the abolition or reduction of standing armies and for the holding and promotion of peace congresses."

Asked if the committee had stretched the limits of the prize that already recognizes human rights advocacy and peacekeeping, Professor Mjoes, a physician and former president of the University of Tromsoe , replied, speaking in Norweigan: "It is clear that with this award, we have expanded the term peace to encompass environmental questions related to our beloved earth." And in his prepared statement, he added, "Peace on earth depends on our ability to secure our living environment."

Ms. Maathai, 64, born in Nyeri , Kenya , founded the Green Belt Movement in 1977, to organize poor women in rural Kenya to plant millions of trees to combat deforestation and to replenish the source of fuel for cooking fires in villages. She is divorced with three children.

The African activist received degrees in science from Mount St. Scholastica College in Kansas , the University of Pittsburgh and the University of Nairobi , where she was awarded a doctorate before directing the veterinary medicine faculty there, according to a biography.

"Maathai stands at the front of the fight to promote ecologically viable social, economic and cultural development in Kenya and in Africa ," Professor Mjoes said.

"She has taken a holistic approach to sustainable development and embraces democracy, human rights and women's rights in particular," he said, adding, "She thinks globally and acts locally."

An activist at home — beaten and jailed during the rule of President Daniel Arap Moi for challenging state policies that threatened Kenyas parks, wildlife and forests — she also traveled broadly to support women's causes.

"Maathai stood up courageously against the former oppressive regime in Kenya ," the Nobel committee said. "Her unique forms of action have contributed to drawing attention to political oppression."

In 1995, at the Fourth World Conference on Women in Beijing , she joined the late Bella Abzug, her longtime activist friend from New York , and a thousand other women in a march to draw attention to the problem of violence against women around the world.

Among a crowd of women dressed in black, she stood out wearing a bright yellow print dress in a procession that was carefully controlled by the Chinese police trying to prevent it from reaching Tiananmen Square , the parade ground where prodemocracy Chinese students were gunned down in June 1989.

"I decided not to wear black, because I am black," she told a reporter, using her characteristic bravura to demonstrate a passionate commitment to women's rights:

"No matter how much we fail, we must recognize that there is hope. Especially in my region, with all the recent slaughter in Rwanda , for even there, the sun will rise, and we continue to hope that we can overcome our suffering."

In 1996, when an international agricultural research organization identified poor farmers in the developing world as a significant threat to forest lands, Ms. Maathai spoke out, saying, "It is very common for people making such conclusions to blame poor people. Poor people are the victims, not the cause.

"In Kenya at the moment, we are fighting to protect the remaining very few indigenous forests from some of the richest people in the country."

Now she will be one of the richest people in the country after collecting the $1.36 million prize at a ceremony in Oslo on Dec. 10, the anniversary of Mr. Nobel's death.

"I am completely, completely overwhelmed," Ms. Maathai told Norway 's TV2 station, which was the first to reach her in Kenya . "That's a lot of money," she said. "I've not had so much money in my life. It's so much I don't know what I'll be able to do with it. But I do know it will go to improve the work we do."

Later in the day, accompanied by President Mwai Kibaki, she appeared at State House wearing a bright green and yellow dress. After President Moi lost power in the 2002 elections, she won a seat in parliament and serves as assistant minister for environment.

"It's a great honor, on me, on my country, on my colleagues, on my friends and all my partners throughout the world," she told supporters. Later, in an interview, she added that "We have changed the way people think about the environment in this country."

She said she was not surprised that the Nobel committee was interested in focusing on environmental issues as an aspect of peace.

"People are fighting over water, over food and over other natural resources," she said. "When our resources become scarce, we fight over them. In managing our resources and in sustainable development, we plant the seeds of peace."

Ms. Maathai is the 12th woman to win the prize in its history. The current Nobel committee, a five-member panel appointed by the Norwegian parliament in early 2003, has three women members.

Geir Lundestad, the director of the Nobel Institute and secretary to the committee, said there were a record 194 nominations for the prize this year. A great deal of speculation had focused on the nomination of the International Atomic Energy Agency and its director, Mohammad ElBaradei, for their efforts in reducing the risks of nuclear proliferation.

Other nominees included Sam Nunn and Richard Lugar who, as members of the United States Senate, conceived a series of programs to control, convert or destroy the nuclear stockpiles of the former Soviet Union .

Nonetheless, Africa 's plight in the modern era of genocidal conflict on the continent; an epidemic from the human immunodeficiency virus; poor government and continuing poverty, compelled the Nobel committee to honor Ms. Maathai's uplifting example.

"When there is so much bad news about Africa ," Professor Lundestad said, "we are happy we could point to a person who provides guidance for the future."

But committee members seemed aware that focusing on the environment might seem a diversion in a world seized by threat of terrorism, nuclear proliferation and war in the Middle East .

Professor Lundestad said committee members were unable to use the prize to encourage any peace process in the Holy Land or in Iraq because so little diplomatic activity is under way.

"I think most people will understand why we didn't award a prize in the Middle East ," said Professor Lundestad. "There has to be a basis of achievement, you cannot just throw out the prize and hope something happens in that crucial region. We hope the situation will get better and we will then have a chance to address the Middle East issue."

For now, he added, "We want to give some hope to Africa ."

The Kenyan government that once persecuted Ms. Maathai was delighted today.

"We are in the mood to celebrate," President Kibaki said in Nairobi .