UPDATE 1-Mexico June oil output down 11.1 pct vs year ago

* June output falls 11.1 pct vs year ago

* Planned maintenance cuts 45,800 bpd

* Export volumes decline 12.7 pct (Recasts, adds details)

MEXICO CITY, July 24 (Reuters) - Mexican oil output fell below 2.6 million barrels per day for the first time since 1990 in June, hit by the relentless decline of the Cantarell field and maintenance, state oil monopoly Pemex said on Friday.

Oil production slid 11.1 percent compared to June 2008 to 2.519 million bpd. Exports of crude were down 12.7 percent at 1.236 million bpd over the same period, Pemex said.

The slide in production has prompted bond rating agencies to warn that the country's debt rating could be cut due to the government's heavy reliance on oil revenues.

Falling oil output has compounded the government's fiscal problems as it wrestles with a severe economic downturn that could be Mexico's worst recession since the Great Depression.

Output from Cantarell, once one of the world's most prolific oil fields, was 658,700 bpd in June, down 37 percent from a year ago. In addition to the natural decline of the field, planned work on a production platform at Cantarell in June cut output by 5,800 bpd.

Work at another offshore oil complex, the Ku Maloob Zaap oil field, trimmed another 40,000 bpd from Mexican output in June.

Gasoline imports were slightly lower at 375,600 bpd in June compared to 376,200 bpd a year earlier.

BANKING ON CHICONTEPEC

Pemex officials say the company remains capable of meeting its goal of producing 2.7 million bpd by the end of the year when new wells come into production but analysts are skeptical the Pemex will be able to reverse the trend of steady declines.

The company says new wells at Chicontepec, a technically challenging unconventional oil deposit where billions of barrels of crude are tightly locked in small pockets, will turn around Mexico's dismal oil production outlook.

Chicontepec produced approximately 30,000 bpd in June and Pemex is aiming to lift output from the area to over 70,000 bpd by the end of the year. But analysts question Pemex's mastery over the challenges of producing oil there.

Pemex's plans call for drilling 1,000 wells a year at Chicontepec to help stabilize oil production until hoped-for oil discoveries in the deep waters of the Gulf of Mexico can be started up sometime in the middle of the next decade. (Reporting by Robert Campbell; Editing by Christian Wiessner)