* Some senior officials question huge investment

* Pemex counting on Chicontepec to stop oil decline

* Output from the area falling short of target

By Robert Campbell

MEXICO CITY, Aug 10 (Reuters) - The multibillion-dollar megaproject that Mexico hopes will turn around its slumping oil industry is being questioned by some officials as results fall short, according to a source familiar with the issue.

State oil monopoly Pemex [PEMX.UL] has banked on an $11 billion plan to tap the unconventional Chicontepec crude deposit to shore up output as yields at other fields plummet, sending Mexican oil production to near 20-year lows.

However, Chicontepec was producing only 30,800 barrels per day in June, a modest rise from December. After years of missed targets and with $3.4 billion already sunk into the project by the end of last year, grumbling about its cost is growing.

"They are coming under a lot of pressure because some people in the government are unhappy with the results. They have spent a lot of money and people are wondering why there is not more oil," the source said, echoing private remarks made recently by several government officials.

The source declined to be identified due to an ongoing working relationship with Pemex.