The National Zoo announced Monday that philanthropist David M. Rubenstein is donating $4.5 million to its giant panda reproduction program, bolstering the zoo’s ability to maintain one of Washington’s most popular attractions at a time of economic strain.

The donation, which Rubenstein described as a holiday gift to the zoo and the city, will cover the tab for five years of giant panda reproduction efforts and for other panda research here and in China. The pandas, on loan from China, previously had their stay extended through 2015, but the zoo had been having trouble securing corporate sponsorship for a program that has delighted and captivated zoogoers for more than a decade.

Now, zoo officials can stop worrying about fundraising for the pandas and turn to what they consider a far more important task: The often frustrating effort to produce panda cubs. The zoo has said that 2012 is probably the last year it will try to achieve a pregnancy with its current pair of giant pandas.

Officials announced the donation during a news conference at the zoo, attended by, among others, Rubenstein; the Chinese ambassador to the United States, Zhang Yesui; the secretary of the Smithsonian Institution, Wayne Clough; and National Zoo Director Dennis W. Kelly.

Kelly described the gift as “an extraordinary act of generosity.”

“Around the world David is well known as an astute businessman, a great community leader, and a great, generous donor,” Kelly said Monday. “Today, David, we’re going to add a new title to your resume: panda enthusiast.”

Clough announced that in honor of the gift the zoo’s Giant Panda habitat was being named the David M. Rubenstein Family Giant Panda Habitat.

Rubenstein is a co-founder and managing director of the Carlyle Group, a global asset-management firm. He is also a member of the board of regents at the Smithsonian, which operates the zoo, and chairman of Washington’s John F. Kennedy Center for the Performing Arts.

The Carlyle Group has $148 billion in assets under management, according to its Web site.

Rubenstein emphasized that this is a personal gift. “It’s my family’s money,” he said. “It’s something that my family wanted to do for Washington.”

This year, the zoo reached a new lease agreement with China that extends the stay of its two popular giant pandas — Mei Xiang, 13, a female, and Tian Tian, 14, a male — for five years. The agreement replaced a 10-year lease that expired late last year. The new agreement expires Dec. 6, 2015.

Giant pandas are native to China, and the Chinese own and lease all giant pandas held at U.S. zoos.

Among other things, the new agreement lowered the annual cost of leasing the pandas from $1 million to about $500,000 — still a substantial sum that the zoo was struggling to raise in difficult economic times.

Rubenstein’s gift — in five $900,000 annual increments — will cover that cost and the cost of continuing giant panda research in the United States and abroad.

In a telephone interview Sunday, Rubenstein said that at a recent meeting of the Smithsonian regents, he was surprised to hear Kelly report that the zoo was having trouble raising money to help pay for the pandas.

“He wasn’t asking for money,” Rubenstein said. “He thought that U.S. companies that might be interested in some China relationship would be interested, but he said he’d not had a lot of success.”

“When I heard about it,” Rubenstein said, “I thought . . . ‘We have been residents of Washington for a long time. We took our children to the zoo when they were younger. I’m a Smithsonian regent.’ And I thought it would be a nice holiday gift for the zoo and people in Washington.”

Worldwide, there are believed to be only 1,600 pandas surviving in the wild, all in the wilderness of China, and a few hundred more in captivity.

Kelly, the zoo director, has said the zoo wants very much to produce more cubs and will try again soon.

If no pregnancy is achieved next year, the new agreement could allow the zoo to request one or more replacement pandas from China, officials have said.

Zoos in Atlanta and San Diego have had more success breeding pandas in recent years.

The National Zoo has produced one cub in 10 years, the beloved Tai Shan, who was born in 2005 and moved from the zoo to a breeding program in China last year.

The zoo’s pandas — both born at the China Research and Conservation Center for the Giant Panda in Wolong, Sichuan province — arrived in Washington on Dec. 6, 2000. At the time, there was hope that they would produce many cubs.

But giant panda reproduction is complex, and in recent years, zoo experts have tried in vain — using natural and artificial methods — to impregnate Mei Xiang.

Recent science suggests that if a female giant panda has not become pregnant for several years, it is unlikely that she will be able to do so.

Still, the zoo is about to try again. Female giant pandas usually go into heat for a brief period of a few days. Mei Xiang, who has gone into heat in early winter the past two years, may be doing so again.

Zoo officials said they have recently detected “power walking” in Tian Tian, an indication that he may sense his mate approaching estrus. When that happens, the two will be allowed to try to mate naturally, something they have not been able to do successfully. (Tai Shan was conceived through artificial insemination.)

If they are unsuccessful, Mei Xiang will be artificially inseminated again. If that doesn’t work, the zoo can explore the possibility of replacement giant pandas with the Chinese, officials have said.

Rubenstein, who grew up in a working-class family in Baltimore, has said he supports closer economic cooperation with China, and he has urged the United States to make it easier for China to invest here.

He has been a major benefactor of the Kennedy Center, reportedly donating, among other things, a new organ for the concert hall.

In 2007, Rubenstein paid $21.3 million for a 700-year-old version of the Magna Carta, a medieval English bill of rights, and placed it on permanent loan to the National Archives.

He has also given millions of dollars to Harvard, Johns Hopkins and Duke universities.