CAIRO (Reuters) - Egypt's stock exchange said on Sunday a subsidiary of Russian billionaire Mikhail Fridman's Altimo had offered to buy 100 percent of Egypt's Orascom Telecom (>> Orascom Telecom Holdings (S.A.E)).

The $3.7 billion offer from a Cyprus-based firm owned by Altimo is at a price of $0.70 per share for all of Orascom Telecom's 5.245 billion shares, the statement said.

"The authority is currently studying the announced offer," the Egyptian Financial Supervisory Authority said in a statement.

Cairo-based Orascom Telecom, a heavyweight on the Egyptian Stock Exchange, is controlled by Russia's Vimpelcom (>> VimpelCom Ltd (ADR)). Altimo owns 47.85 percent of Vimpelcom.

Orascom Telecom is the third large firm that is taking steps to leave the Egyptian market this year. In February, Egypt's regulator approved an offer by Qatar National Bank (QNB) (>> Qatar National Bank SAQ) to acquire Cairo's National Societe General Bank (NSGB) (>> National Societe Generale Bank).

Orascom Construction Industries (OCI) (>> Orascom Construction Industries SAE) is also finalising a deal with its Dutch-listed parent company OCI NV (>> OCI) that may lead it to leave the Egyptian stock exchange.

"It will affect the index market capital which is already impacted by NSGB exiting and OCI, which might happen anytime now, so we are talking about more than 25 percent of the weight of the index," said Ahmed Adel, telecom analyst at Naeem Brokerage.

"The biggest players in the Egyptian market are OCI and Orascom Telecom and NSGB, and the idea is given the market conditions and the political situation ... you cannot expect a high flow of new listings in the index right now," he added.

(Reporting by Asma Alsharif,; Editing by Catherine Evans, Bernard Orr)