Another cloud could be on the horizon for ambitious Bermuda undersea cable operator Global Crossing, threatening its looming $11.1 billion takeover bid.

A stock slide has seen the company's shares dip below $34.56 -- the level at which target company Frontier could be entitled to walk away -- but Global Crossing's CEO is still "confident'' the deal will go through.

Global Crossing has already fought off rival company Qwest Communications in the fight for Rochester New York-based long distance carrier Frontier, by surrendering another proposed acquisition, Denver-based Baby Bell US West.

The Frontier deal remains on track to close in late September. But it seems the deal could be undermined according to a get-out in the contract which can be activated if Global Crossing's average share price dips lower than $34.56 over 15 randomly selected days in a period before closing.

Apparently the shares have not closed above this level since August 5.

But this has not dampened the outlook of CEO Robert Annunziata.

"I feel pretty confident we'll be closing,'' he said, adding that he foresaw little or no adjustment to the deal which he thought would hold as is.

Other Global Crossing chiefs have been quoted in US and Canadian reports suggesting that the company could always boost its offer with additional stock or cash, if needed.

At the Telecom Business '99 conference in New York this week Mr. Annunziata said his company's move to back down to Qwest over the takeover of US West rather than sparking a bidding war showed admirable financial restraint.

"We did not believe our best interest would be served by adding about $5 billion to our offer,'' he said.

In summing up Global Crossing's tactic he said: "Our two-pronged strategy is to build what we can and to buy what we must.

"We are moving rapidly to take advantage of an emerging market opportunity.'' And he said Frontier would form a vital link in the system. Yesterday Global Crossing announced it had completed the first upgrade of its Atlantic Crossing 1 transatlantic cable system which will carry voice and data transmissions.

The capacity was doubled to meet trans-Atlantic demand. It was improved to carry 80 gigabits per second and the upgrading was completed 18 months ahead of the original planned time, the company said.

A second upgrade will raise capacity to 140 gigabits per second by March next year.