UPDATE 1-S.Korea firms to invest $12 bln in oil, gas development next yr -gov't

* Record-high planned investment up 34 pct from 2011 estimate

* Competition for natural resources seen increasing -econ minister

* KOGAS set to join Iraq's 4th oil, gas bidding round in March (Adds details, quotes)

SEOUL, Dec 21 (Reuters) - Over 50 state-run and private firms in South Korea, heavily dependent on energy imports, plan to invest a record-high combined $11.8 billion next year to develop oil and gas resources, the ministry of knowledge economy said on Wednesday.

The world's fifth-largest crude oil importer and second-largest liquefied natural gas (LNG) buyer has been boosting overseas resources development as like regional peers it grapples with inflation driven by costlier energy and commodities.

The total investment, almost all of which will be made overseas, would be a 34 percent increase from the estimated $8.8 billion invested this year, the ministry said in a statement.

"Next year competition to secure resources will be more severe, and uncertainty in resources supply is expected to rise due to the financial crisis in Europe, economic slowdown in developed countries, and changes in the energy mix since Japan's nuclear crisis," the statement quoted knowledge economy minister Hong Suk-woo as saying.

Three public firms including Korea National Oil Corp (KNOC), Korea Gas Corp (KOGAS) and Korea Electric Power Corp (KEPCO) account for $7.8 billion of the planned investment, the ministry said.

The remainder will come from 49 private firms including SK Innovation, which owns the country's largest crude oil refiner SK Energy, GS Energy and LG International Corp , the statement said.

KOGAS, the world's largest corporate buyer of LNG, is preparing to participate in Iraq's fourth bidding round for its oil and gas fields, scheduled for March 2012, the statement added.

It added that state-run utility KEPCO planned to boost coal and uranium supplies.

A spokesman at state-run KNOC said earlier this month that the firm aims to invest between $3 billion and $4 billion next year to acquire overseas oil assets and beef up daily oil production. (Reporting by Cho Mee-young; Editing by Jonathan Hopfner)