UPDATE 1-Mexico gross fixed investment up 3.3 pct in Dec

(Adds details on sectors, adds context)

MEXICO CITY, March 7 (Reuters) - Mexican gross fixed investment, a measure of spending on machinery, equipment and construction, rose a weak 3.3 percent in December from the year-ago period, the government said on Wednesday.

The number was well below the 5.96 percent median increase forecast by analysts in a Reuters poll ECONMX.

On a seasonally-adjusted basis, gross fixed investment rose 1.37 percent in December versus November.

Investment in machinery and equipment increased 2.5 percent year-on-year, with investment in imported products up 4.6 percent and spending on domestically made products down 1.7 percent.

Construction investment rose 4.3 percent.

Mexico's economy grew at a healthy 4.8 percent in 2006, helped by robust industry, services, exports and consumer demand, but growth is expected to lose steam due to a slowdown in the United States, Mexico's main trading partner.