WASHINGTON (Reuters) - The number of U.S. workers seeking jobless benefits rose by an unexpectedly steep 12,000 last week to 321,000, government data showed on Wednesday, but remained at levels pointing to a healthy labor market.

The latest figures from the Labor Department cover the week ending Nov. 18 and compare with Wall Street forecasts for claims of 310,000. This follows a revised 309,000 the week before, initially reported as 308,000 applications for aid.

"So far, jobless claims remain extraordinarily low despite a rapidly deteriorating housing market and a weakening manufacturing sector. The economic growth remains intact," said Mark Zandi, chief economist at Moody's Economy.com in West Chester, Pennsylvania.

"This is an important leading indicator of payroll employment, and payroll employment is the best coincident measure of economic activity. It seems from this latest report that the payroll employment gain in November will be near 150,000 jobs," he said. --------------- Wage pressures

The labor market is under close scrutiny after a surprise drop in the unemployment rate to 4.4 percent in October, from 4.6 percent, after 92,000 fresh jobs were created that month.

Federal Reserve officials may worry a tight labor market could add to wage pressures as they consider whether to keep interest rates on hold at their next meeting, on Dec. 12.

November's jobs situation will be reported on Dec. 8.

Slowing U.S. growth in the third quarter has led some economists to predict a deterioration in labor market conditions in the months ahead.

"The weekly initial claims data are a little worse than expected," said Action Economics in a note to clients.

"(This) suggest some risk to our 135,000 forecast for nonfarm payrolls. The data could add downside pressure on the dollar and yields amid thin trading," it noted.

A Labor Department official said there were no special factors accounting for the increase in claims last week.

The four-week moving average -- seen as a more reliable gauge of underlying employment trends -- rose to 317,000 compared with 314,000 the week before.

People who remained on the benefits rolls after drawing an initial week of aid increased by 14,000 to 2.454 million in the week ended Nov. 11, the latest week for which data are available. Analysts had forecast 2.43 million claims.

"The trend in jobless claims ought soon to start rising, given the clear slowdown in growth, and the recent numbers might mark the start of the cyclical move," said Ian Shepherdson, chief U.S. economist at High Frequency Economics in a note to clients. ----------- Housing slowdown

In other data released on Wednesday, U.S. mortgage applications fell for the first time in three weeks despite a dip in mortgage rates to their lowest level since January.

The Mortgage Bankers Association said its seasonally adjusted index of mortgage application activity, which includes both refinancing and purchasing loans, for the week ended Nov. 17 fell 3.7 percent to 623.6 from the previous week's 647.5.

A cooling housing market has raised fears the U.S. economy may be heading for trouble, with some investors betting the Fed will have to cut rates next year as growth slows.

In fact, the latest Reuters poll forecast the U.S. central bank would lower rates by the middle of next year.

Median forecasts in the survey of 60 economists showed the Fed's next move will be to cut the federal funds rate to 5.0 percent, from 5.25 percent now, by mid-2007 while the odds of the economy sliding into recession in 2007 was seen at about 1 in 4.