The producer price index for inputs to construction increased 0.9 percent in both September and August, while the indexes that reflect what contractors would charge for their work were largely unchanged. The price increases for materials follow several months of declining prices, so that the year-over-year change in the index for materials was a “deceptively mild 1.7 percent,” said Simonson.

The economist cited rising prices for a variety of essential construction materials as responsible for the recent spike. The price index for diesel fuel jumped 5.7 percent in September, following a leap of 8.7 percent in August. Prices for copper and brass mill shapes climbed 3.6 percent in September. The indexes for aluminum mill shapes and lumber and plywood each rose 1.1 percent in the latest month, while the price of steel mill products increased 1 percent.

AGC officials said inadequate public investment in infrastructure is a major reason contractors are unable to recover costs.

“With so few projects to bid on, contractors are offering their services with little or no margin to cover materials costs,” said Stephen E. Sandherr, the association’s chief executive officer, noting that recent Census Bureau data showed a 3.5 percent drop in public construction spending from August 2011 to August 2012. “Despite the tepid recover, the construction industry continues to suffer from tight margins and weak demand. That is why federal, state and local agencies must keep funding intact for construction, or they will have even worse problems with unemployment and shuttered businesses.”