* Leading indicator falls to 1.28 in Dec
* Construction activity loses momentum
* Swiss PMI data due at 0830 GMT
ZURICH, Jan 3 Switzerland's economic momentum cooled for a third straight month in December and by more than expected as weakness in the neighbouring euro zone weighed on business confidence, a leading indicator showed on Thursday.
The KOF barometer, a gauge of the Swiss economy's performance in about six months' time, fell to 1.28 points in December from 1.50 points in November, the KOF Swiss Economic Institute said.
The reading missed analyst expectations, which averaged 1.35 in a Reuters poll..
"In comparison to previous months the cooling trend gathered some momentum in December. The prospects for the Swiss economy are noticeably bleaker in the new year," the KOF said in a statement.
The economy grew faster-than-expected in the third quarter of 2012 but the Swiss National Bank said at its rate-setting session last month that it expected growth to significantly weaken in the final three months of 2012 as the global economy remained fragile.
Data on the manufacturing sector is due at 0830 GMT . In November industrial production grew at a rate not seen since early 2011 as manufacturers were surprised by an upturn in demand. (Editing by Susan Fenton)