SAINT VINCENT, Ark. (AP) _ One of two liquid fuel components used in Titan II missiles leaked Tuesday as crews deactivated a silo, causing an orange vapor cloud and prompting the temporary evacuation of several families, the Air Force said.

No injuries were reported at the site about 1 1/2 miles north of Saint Vincent, said Capt. James Smith of the 308th Strategic Missile Wing at Little Rock Air Force Base at Jacksonville.

The oxidizer is one of two liquid fuel components used in the aging missiles. The Pentagon has ordered that missiles in Arkansas, Arizona and Kansas be deactivated.

The leak occurred as workers removed the oxidizer from the missile through fuel lines, Smith said.

''The fuel lines were still hooked up from missile to trailer, and we had to purge those lines,'' he said. ''The unit actually burped and some liquid fell on the ground, forming an orange cloud.''

Crew members wore environmental control suits and were not injured, Smith said.

Six families who live in the area were evacuated for about two hours. They were allowed to return when tests showed no contamination.

Eight Titan II silos are still in operation in Arkansas, Smith said.

A leak at a Titan II silo at Damascus, about 20 miles east of Saint Vincent, caused an explosion Sept. 19, 1980, that killed one crewman and injured 21 others.