and maids a-milking are driving up the price of a traditional Christmas. The cost of buying the gifts in "The Twelve Days of Christmas'' song rose 5.7 percent this year to $13,196 from $12,482, according to the annual Christmas Price Index calculated by PNC Bank Corp. For purists who total up all 12 partridges, 12 pear trees and every other item mentioned in all dozen verses, the true cost rose to $54,478 from $51,765. Blame it on the Philadelphia Dance Company, whose performance fees rose for the first time in four years, pushing up the cost of nine ladies dancing by 25 percent. As for 10 lords a-leaping (dancers from the Pennsylvania Ballet doing leaps in lordly attire), their salaries held constant this year, but should rise under a provision of a new labor contract, PNC economist Rebekah McCahan Fickling says. Milkmaids come cheap, yet less so than last year. The cost of an hour of milking by eight maids this year rose 11.8 percent to $38, reflecting the higher hourly minimum wage. Cows aren't included. The index mirrors rising wages in the service side of the economy, says Patrick Bradley of PNC's asset-management group, which has compiled the index since 1984. "That isn't to say there aren't productivity increases'' in this sector, he says, quick to defend the dancing ladies and milkmaids, only that "statistics measure them poorly.'' This year's spurt in the Christmas index exceeds the overall inflation rate of 2.8 percent for the first nine months of 1996, according to the U.S. Consumer Price Index. And it follows a nearly 22 percent decline last Christmas, when prices of pear trees, gold rings and swans, especially, took a dive. Still the index's chief luxury item, swans are selling at a deep discount. After dropping 50 percent last year, the price the Philadelphia Zoo quotes for seven long-necked trumpeter swans held constant at $3,500, the result of more successful breeding in captivity. The price of five 14-karat gold wedding bands also was unchanged this year, at $325 at a Philadelphia jewelry store, following a 28 percent decline last year. (Tastes are shifting toward gems in wedding bands, it seems.) And the price of a pear tree remained $12.50, following a decrease of more than 37 percent in 1995. So for all of you with a little excess cash to burn, or if you're interested in giving a loved one the gift of a lifetime at what is actually a steal at just over $13,000, you know where to start shopping. PHOTO The cost of nine ladies dancing helped raise the price of items in `The 12 Days of Christmas', 5.7 percent, to $13,196