WASHINGTON, Jan 3 (Reuters) - U.S. construction spending increased in November amid strong gains in single-family homebuilding, but outlays on public projects were weak. The Commerce Department said on Monday that construction spending rose 0.4% after a similar advance in October. Economists polled by Reuters had forecast construction spending climbing 0.6%. Construction spending increased 9.3% on a year-on-year basis in November. Spending on private construction projects rose 0.6% in November. Outlays on residential construction surged 0.9%. Single-family homebuilding spending shot up 1.2%, but outlays on multi-family housing projects dipped 0.3%. Homebuilding remains constrained by shortages, which are boosting prices of building materials. Residential investment contracted for a second straight quarter in the third quarter, weighed down by decreases in home improvements and single-family homebuilding. Investment in private non-residential structures like gas and oil well drilling edged up 0.1% in November. Spending on structures declined for a second straight quarter in the July-September period, led by commercial and healthcare structures. Spending on public construction projects fell 0.2% in November. Outlays on state and local government construction projects dropped 0.2%, while federal government spending decreased 0.4%.