MUMBAI, April 12 (Reuters) - Investment firm GQG Partners and State Bank of India Mutual Fund are considering investing up to $800 million in total in a $2.16 billion share offering of Indian telecom firm Vodafone Idea, according to two people familiar with the matter.

U.S.-based GQG, run by India-born executive Rajiv Jain, plans to invest about $500 million, while SBI Mutual Fund is considering an investment of $200-300 million in the follow-on public offering, said both people, who declined to be named as the plans are confidential.

GQG and SBI declined to comment while Vodafone Idea did not respond to queries seeking comment.

Debt-saddled Vodafone Idea was formed in 2018 when Vodafone Group merged its India business with local billionaire Idea Cellular in a $23 billion deal.

The company, in which Vodafone has more than 25%, is India's third biggest operator after Reliance Jio and Bharti Airtel , who have taken away its market share in recent years.

It said earlier on Friday said the sale of new shares will run from April 18 to April 22.

GQG and SBI Mutual Fund are considering investments under the institutional quota of what will be India's biggest secondary offering. A final decision on their investments has not been reached.

Vodafone Idea plans to use the funds to expand its 4G network, set up 5G networks, pay taxes and dues, it said in its regulatory filing this week.

(Reporting by M. Sriram; Editing by Aditya Kalra and Tomasz Janowski)