MEXICO CITY (Reuters) - Shares of Mexico's Cemex, the world's No. 3 cement maker, fell hard on Friday after its quarterly earnings guidance disappointed investors worried about the impact of the U.S. economic slowdown.

Cemex's New York-traded stock (CX.N: Quote, Profile, Research) lost 9.75 percent to $25.47 and its local shares dropped 8.36 percent to 27.75 pesos.

Cemex (CMXCPO.MX: Quote, Profile, Research) said on Thursday it expects earnings before interest, taxes, depreciation and amortization, or EBITDA, of $920 million in the first quarter, 6 percent higher than the year-ago period.

That was lower than expected by analysts, who are worried about the impact of a downturn in the U.S. housing market at and possible recession in the United States.

Credit Suisse cut its rating on shares of Cemex, which generates about a fifth of its sales in the United States, to "neutral" from "overweight" following the guidance.

"We see a significant deterioration across Cemex markets, namely the United States and Spain," Credit Suisse said.

Investors have been concerned that the July acquisition of Australia's Rinker Group might broaden the Mexican company's exposure to the anemic U.S. market, hit by a mortgage credit crisis.

BBVA Bancomer said despite the lackluster guidance, Cemex remains attractive. It recommended buying the company at current prices.

Cemex shares have lost close to 40 percent of their value since mid-2007, when they were at an all-time high.

(Reporting by Noel Randewich, editing by Leslie Gevirtz)