President Reagan is walking around with his pants legs tucked into his boots and heeding warnings not to handle dead animals following the discovery of a wood rat infected with bubonic plague about a mile from Reagan's California ranch, White House deputy press secretary Larry Speakes said today.

The White House press corps, having little else to write about, leaped on the plague story.

The threat to the president appeared remote. Not since an apparently crazed rabbit launched am amphibious attack on President Carter in a Georgia pond has the animal kingdom posed such a threat to a chief executive.

Only one infected rat has been found, but health authorities have posted plague warning signs on trees throughout the Santa Ynez mountains around the Reagan ranch. The signs urge that pets be kept on leashes, pants be tucked in and warn against handling any wild animals -- dead or alive.

Like most people, the president has no known fondness for picking up dead animals, so complying with the warnings has not interfered with his normal vacation life centering on horseback riding, cleaning brush and cutting wood.

Bubonic plague, which was a terrifying killer disease in the Middle Ages, can be transmitted by fleas as well as by contact with infected animals.

The president was advised of the infected rat shortly before leaving Washington for his four-week stay in California and did not consider altering his vacation plans, Speakes said.

Reagan and Nancy Reagan spent another quiet day at their 688-acre Rancho Del Cielo (ranch in the sky), undisturbed by the animal kingdom and equally untroubled by a group of striking air traffic controllers at the ranch gate. The group canceled its plans to picket after the Park Service told the controllers the area was dry and that a demonstration would pose a fire hazzard.

As controversy continued over how safe it is to fly during the strike, Speakes reiterated the White House position: "We're fully satisfied that it's as safe to fly now as it ever was."