* What: Cemex first-quarter earnings survey

* When: Scheduled to report April 21

* Net profit seen up 9.5 percent to $438 million

MONTERREY, Mexico (Reuters) - Mexico's Cemex, the world's No. 3 cement maker, is expected to report a 9.5 percent rise in first-quarter earnings on Monday as an asset sale helps offset the negative impact of the U.S. housing crisis.

Six analysts polled by Reuters forecast, on average, net profit of $438 million, up from $400 million in the year-earlier first quarter.

The analysts said Cemex's (CMXCPO.MX: Quote, Profile, Research) (CX.N: Quote, Profile, Research) sale of its 9.5 percent state in local telecoms company Axtel (AXTELCPO.MX: Quote, Profile, Research) in late March for $257 million would help the results.

"The net profit could be surprisingly positive because of the extraordinary gain from the Axtel share sale," BBVA Bancomer said in a note.

That is welcome money, given that in March Monterrey-based Cemex, which has operations in over 50 countries, said its cement sales volumes in its key markets of the United States, Mexico and Spain all fell in the first quarter.

Cemex, which acquired Australian rival Rinker for $16 billion last year, competes globally with Switzerland's Holcim (HOLN.VX: Quote, Profile, Research) and France's Lafarge (LAFP.PA: Quote, Profile, Research). It has been hit by the slump in residential construction in the United States, a slowdown in the Mexican economy, and a drop in housing demand in Spain.