BOSTON -- The Franklin Park Zoo, the only Boston institution of its kind, may be forced to close and euthanize some of its animals, zoo officials said Friday.

Without more state funding, zoo officials said that they will run out of money within months and have to close both Franklin Park and the Stone Zoo in Stoneham.

The zoos would be forced to lay off most of their 165 employees and attempt to find new homes for more than 1,000 animals.

Zoo officials estimated 20 percent of the animals would not find homes and could be euthanized.

“Not all the animals in the collection will be able to be placed at other facilities,” John Linehan, zoo president, wrote in a letter to the Massachusetts Legislature. “The Commonwealth would then be forced to either continue to maintain the animals in the closed facilities or euthanize them.”

The Legislature had originally provided $6.5 million to the zoos, but Gov. Deval Patrick cut the state funding to $2.5 million.

"Like families throughout the Commonwealth, the state must cut back and the $4 million reduction to the zoo budget is just one example of spending decisions we've made to live within our means," said Kyle Sullivan, a spokesman for Patrick.

Patrick said he has asked state officials to work with the zoo to ensure the safety and well-being of all the animals. The zoo said it had no plans to euthanize any animals unless it is forced to close.

The Franklin Park Zoo was founded in 1913. It is funded by state money, private donations and revenue from the attractions.