UPDATE 1-Mexico's Pemex capex to average $27 bln per yr

(Adds background on Calderon, Mexican oil industry, paragraphs 3-6)

MEXICO CITY Aug 30 (Reuters) - Mexico's state oil company Pemex aims to lift capital investment to an average $26.8 billion a year through 2019, Chief Executive Juan Jose Suarez said on Monday.

Pemex's [PEMX.UL] capital spending is expected to be approximately $20 billion this year.

Mexican President Felipe Calderon will outline his government's spending priorities for next year when the finance ministry unveils its 2011 budget proposal in early September.

Mexico, which nationalized its oil industry in 1938 and created state monopoly Pemex, is a top supplier of crude to the United States. But years of underinvestment have left it unable to counter a fall in output since 2004.

Pemex says there could be huge undiscovered oil deposits in the deep waters of the Gulf of Mexico, but the company lacks the technology and budget to be able to be producing there any time soon. Mexico's Constitution bans foreign direct investment in the energy sector, which keeps major oil companies out of strategic ventures in Mexican crude exploration or production.

Calderon's conservative party wants more private investment in energy, but given opposition in other parties its lawmakers say there is little hope of reforming the sector before 2012. (Reporting by Robert Campbell and Jason Lange; Editing by David Gregorio)