Carlos Acosta lives by the credo: “When you believe in something, you act on it and don’t just pray about it.” So it was no surprise to see him serving as maitre d’ at the Christmas dinner for hundreds of families from homeless shelters in the Washington Heights area who came in shifts to St. Elizabeth Queen of Martyrs Roman Catholic Church on Dec. 21. Acosta is well known at UFT headquarters for his warm smile and friendliness as he carves the roast or serves up the sides in the cafeteria, where he works during the week. What UFT members may not know about him is that, when not working, he often hands out food and blankets to the needy and homeless as a kind of street ministry he has conducted since he was 17. Back then, he prepared simple pasta dishes with a friend and distributed them around the 168th Street and Broadway A train subway station, where he knew the homeless congregated in the winter to keep warm. Now married with a 10-year-old son, Acosta — with the help of scores of other youth ministry volunteers he has helped recruit — is able to reach many more needy people each weekend. At Thanksgiving he helped distribute packaged turkey dinners to more than 1,000. For Christmas he helped prepare a formal, family-style, sit-down dinner, “so everyone would feel at home,” he said. Acosta is a graduate of PS 152 in the Bronx and John F. Kennedy HS.