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July 18 (Reuters) - Mortgage giant Freddie Mac (FRE.N: Quote, Profile, Research) is considering raising capital by selling as much as $10 billion in new shares to investors, The Wall Street Journal reported, citing people familiar with the matter.

The report comes after the U.S. Treasury and Federal Reserve announced a plan on Sunday to shore up the balance sheets and borrowing capabilities of Freddie Mac and sister company Fannie Mae (FNM.N: Quote, Profile, Research).

Such a share sale, which has not yet been determined, could forestall a full government rescue, the WSJ said.

Investors, sensing the need for these pillars of the U.S. housing market to raise capital -- and thereby diluting existing shares -- sent their stock prices down more than 60 percent this month alone.

The main buyers for any new-stock issues are likely to be existing shareholders worldwide, the paper said, citing one person involved in the discussion.

Any sale would have to offer a high rate of return to attract buyers, given the near-14 percent yield on Freddie's preference shares, the paper added.

At that rate even a $5 billion preferred-stock offering would mean a company payout of $690 million a year, reducing the money available to common-stock shareholders, cutting the value of those holdings and putting further pressure on the share price.

Shares in Asia .MIAPJ0000PUS extended losses to fall 1.1 percent on Friday after the newspaper report, which added to worries about the stability of the U.S. financial sector.