MCI shares surged 9% Monday after a big investor said it might buy a controlling stake in the struggling telco.

The Ashburn, Va., company said Leucadia National ( LUK) filed with regulators seeking antitrust clearance to buy 50% or more of MCI's stock. Leucadia is already a big player in the wholesale telecommunications market, having taken control last year of Tulsa, Okla., communications outfit WilTel.

The news comes as Wall Street braces for the re-emergence of MCI, which has spent three years on the sidelines following its fraud-induced plunge into Chapter 11. There has been much speculation about a potential rush to buy MCI; rumors have had big telcos such as Sprint ( FON) battling for the right to take over its lucrative big business contracts.

But the festivities have been dampened in recent months by the company's faltering financial results. MCI has repeatedly cut jobs this year in an effort to keep its head above water as prices plunge in the increasingly cutthroat wholesale telecom business.

Last month, TheStreet.com reported that MCI is shutting down its small-business operations and backing out of consumer sales as it prepares to abandon those markets in the wake of an unfavorable pricing ruling.

Meanwhile, MCI continues to try to put its house in order after its long stay in bankruptcy. On Friday the company sued founder and former CEO Bernie Ebbers over hundreds of millions of dollars in loans he failed to repay. Ebbers, who has pleaded innocent to federal fraud charges, is due to stand trial this fall.

On Monday, MCI's pink-sheets-listed shares rose $1.30 to $15.90.

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