In what sounded like a valedictory address, Queen Elizabeth II praised the United Nations as a "force for common good" but said much work still needed to be done.
"It has perhaps always been the case that the waging of peace is the hardest form of leadership of all," the queen said during her first stop on a brief, low-key visit to New York.
"I know of no single formula for success, but over the years I have observed that some attributes of leadership are universal, and are often about finding ways of encouraging people to combine their efforts, their talents, their insights, their enthusiasm and their inspiration, to work together."
Wearing an Angela Kelly pale-blue floral silk dress trimmed with mocha-colored satin and matching hat, the queen stood before diplomats and urged them to confront the challenges of the international community.
"One [challenge] is the struggle against terrorism," the queen said. "Another challenge is climate change, where careful account must be taken of the risks facing smaller, more vulnerable nations, many of them from the Commonwealth."
Diplomats stood and applauded when the queen arrived. Alejandro Wolfe, deputy U.S. ambassador to the United Nations, was the highest-ranking American in the hall to hear the queen's speech.
With nearly 60 years on the throne, the queen is the world's most experienced head of state. Her speech echoed her first U.N. address in 1957 when, at the age of 31, she encouraged diplomats to pursue "the goal of a world at peace, law abiding and prosperous for which men and women have striven so long and which is the heart's desire of every nation here represented."
The queen also placed a wreath at ground zero and formally opened the British Garden of Remembrance in Lower Manhattan in memory of the 67 British victims of the 9/11 attacks. Relatives of some of them met the queen.
"The fact that she's fitted this into her very busy schedule I think is amazing," said Alex Clark, whose child died on 9/11. "We're very proud."
The queen's visit, her first to New York since 1976, came at the end of a nine-day trip to Canada, where she and her husband, the duke of Edinburgh, marked the centenary of the Canadian navy.
Her half-day trip to New York City is short by design, according to royal watchers.
"They are very cost conscious," Majesty magazine editor-in-chief Ingrid Seward said. "She's not overnighting in New York. The queen is 84-years-old. She's had an exhausting nine-day trip. She'd rather be home than stay on in New York."
A short trip is not the only cutting back by the royal family.
Queen Elizabeth has decreased her spending by $4 million in the past year, according to a new report released by the palace. The British government gave $57.8 million in taxpayer dollars to support the royal family. The monarchy costs each British citizen 94 cents.
Alan Reid, keeper of the privy purse, said Monday that the queen and other royals are cutting costs and postponing essential maintenance on the palace, because they are "acutely aware of the difficult economic climate."
The royal family also sold the queen's helicopter, freeing up more money.
The Royal Train, which costs more than $75,000 every time someone travels in it, is now used only by the queen and the duke of Edinburgh, and Prince Charles and his wife, the duchess of Cornwall.