KHOBAR, Saudi Arabia, July 26 (Reuters) - Saudi Aramco will complete the first phase of an expansion of the main gas pipeline across Saudi Arabia by the end of this year, the company said in its weekly magazine, part of an effort to meet the kingdom's rising gas demand.

The Master Gas System (MGS) was built in the mid-1970s to gather and process associated gas from oil wells for domestic industry.

The world's top oil exporter is pressing on with gas-related projects to meet demand and save crude for export and refining.

The pipeline expansion project will help deliver gas to the western region, including the King Abdullah Economic City and the Rabigh 2 independent power plant.

"The first phase will be completed by the end of 2017, increasing the capacity of the MGS to 9.6 billion standard cubic feet per day (scfd). The second phase will bring that capacity up to 12.5 billion scfd in 2019," Saudi Aramco said in its Arabian Sun magazine.

The first phase of the pipeline, in which the contractor will install booster gas compressor stations, was due to be completed by the end of 2016, with phase two finished by 2018, previous reports said.

Saudi Aramco plans to nearly double its gas production to 23 billion standard cubic feet per day over the next decade.

The plans include boosting output at its Hawiyah and Haradh plants. The projects, estimated to cost $4 billion, would expand processing capacity at Hawiyah by 1.3 billion scfd. Hawiyah gas plant now processes 2.5 billion scfd of gas.

(Reporting by Reem Shamseddine; Editing by Edmund Blair) ((Reem.Shamseddine@thomsonreuters.com; +966503335202; Reuters Messaging: reem.shamseddine.thomsonreuters.com@reuters.net))