SAN FRANCISCO -- Warning of "growing environmental problems" on a global scale, Britain's Prince Charles called on a gathering of business and civic leaders in San Francisco Monday to support environmental sustainability.

"We simply cannot go on as we are," the prince told an audience of 300 at an environmental seminar at the Ferry Building.

"Somehow, we have to find the courage to re-assert the once commonplace belief that human beings have a duty to act as the stewards of creation," Charles said.

The talk on environmental issues was the Prince of Wales' only publicly announced speech during his four-day visit to the Bay Area with his wife, Camilla, the Duchess of Cornwall.

The future king has a strong personal interest in environmental matters and in recent years has sponsored environmental charities, started an organic farming enterprise and advocated global cooperation to protect the environment.

The Ferry Building seminar was intended to provide the West Coast introduction of the Prince of Wales's Business and the Environment Programme. Charles founded the project in 1994 to engage business leaders in supporting sustainable development.

He told the group that recent scientific studies have given "stark warnings" of increasing environmental problems, including global warming, over-fishing, loss of forests and declining fresh water aquifers.

One study commissioned by the United Nations concluded that "human activity is putting such strain on the natural functions of the Earth that the ability of the planet's ecosystems to sustain future generations can no longer be taken for granted," he said.

"Addressing all these threats to our long-term survival will clearly require a massive and coordinated response from all sectors of society and in all nations," Charles said.

The prince said technological innovation will help to solve environmental problems, but that care must be taken to ensure that technological breakthroughs help and do not harm the world's poorest and most vulnerable people.

He also cautioned against an assumption that spending money on new technology is always the best solution.

Charles drew applause when he said, "I may not be an economist, but I am a historian, and I would have thought that history suggests that attempting to re-engineer our planet is fraught with danger and that simple solutions are usually the most sustainable."

Simple and sustainable solutions include energy efficiency, organic farming and preventing pollution through good design, the prince suggested.

Charles read his speech while standing at a podium and did not use a teleprompter.

He again drew applause from the business, government and environmental representatives when he urged that the United States use its influence to support an agenda of environmental stewardship.

"The environmental crisis we face is another situation in which I believe the United States could use its power and influence to help create a sense of unity in a common cause among disparate peoples and sectors of society," he said.

"If that were done, the benefits would be felt around the world, and for generations to come," Charles said.

After the speech, Charles, 56, and Camilla, 58, left by motorcade to prepare for their final event of the day, a black-tie dinner at the new de Young Museum in San Francisco's Golden Gate Park.

They arrived at the Ferry Building on a Coast Guard cutter after a morning visit to the Edible Schoolyard, an organic farming and cooking program at the Martin Luther King Middle School in Berkeley.

Before the speech, they visited artisan and organic food shops in the marketplace area of the renovated Ferry Building, including a fruit market, a mushroom market, two Italian delicatessens and a confectionery store where Camilla sampled a brownie.

Charles and Camilla are scheduled to end their eight-day visit to the United States on Tuesday after a morning visit to the Empress Hotel, a project to help homeless people in San Francisco.

The goodwill trip, which also included stops in New York, Washington D.C. and New Orleans, is the couple's first official overseas tour since their wedding in April.

Charles told the Ferry Building gathering at the start of his speech that he was "enormously touched and flattered" by the warm welcome the couple has received in California. He said he was last in San Francisco 29 years ago.

"It's wonderful to be back in this part of the world again and with my darling wife," he said.