Boeing Co shares sank more than 6 percent on Monday as analysts said cuts in production would hurt the plane maker's earnings this year.

After the markets closed on Thursday, Boeing said cuts in output of widebody planes and lower-than-expected airplane prices would reduce first-quarter earnings by about 38 cents a share. Wall Street had been expecting profit of $1.19 a share.

Many analysts pared their share-price targets and earnings estimates for Boeing on Monday.

We think that this is just the first of the cuts that Boeing will have to make to its aircraft production rates as it moves through this downcycle, Macquarie Research analyst Robert Stallard said in a note.

Until there is a recovery in airline demand, profits, financing and confidence, Stallard added, we expect to see further delivery deferrals and probably lower production into 2011.

Chicago-based Boeing said last week that output of its 777 wide-body twin-engine airliner would fall to five planes a month from seven beginning in June 2010. It added that it would postpone modest planned production increases of its 747-8 and 767 widebody model planes.

Boeing said its airline and cargo customers were facing extremely difficult economic times.

Cowen & Co cut its rating on Boeing to underperform from neutral on Monday, saying the rate cuts and lower plane prices would pressure quarterly earnings all year. The firm said it expected Boeing to cut its full-year outlook when it reports earnings on April 22.

Besides facing the prospect of more plane order deferrals or cancellations from airlines and cargo carriers, Boeing could also suffer because of planned program cuts at the U.S. Defense Department, analysts said.

Last week, Defense Secretary Robert Gates announced proposals that would end production of C-17 military transport aircraft, restructure the Army's Future Combat Systems program and terminate the Air Force Combat Search and Rescue X helicopter program, moves that would affect Boeing.

Boeing's defense outlook is weakest among the large primes, based on shifting budget priorities, Sanford Bernstein analyst Douglas Harned said in a research note on Monday.

Gates' recommendations must still become part of President Barack Obama's formal budget submission to Congress, and lawmakers will have the last say on spending.

Shares of Boeing, a component of the Dow Jones Industrial Average <.DJI>, were down $2.43, or 6.2 percent, at $36.72 in morning New York Stock Exchange trading. The stock has fallen about 14 percent this year.

(Reporting by Karen Jacobs; Editing by Lisa Von Ahn)