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Clara Furse, chief executive of the London Stock Exchange, plans to keep Nasdaq at bay, and on Thursday, she put money on it.

Furse has said privately in recent weeks that she would prefer to keep the exchange from Nasdaq’s clutches, and then promote its liberty from U.S. regulators after its rival Euronext pairs up with the New York Stock Exchange.

On Thursday, the London exchange pledged to buy back as much as £250 million, or $493 million, in shares this year, an offer that would increase the exchange’s debt load enough for Moody’s to put the stock on review for a possible downgrade. The London exchange also reiterated that Nasdaq’s offer of £12.43 a share was “wholly inadequate,” and Furse said that she was in talks with other exchanges, but would not specify which.Furse and the London exchange have been under siege since Nasdaq formally initiated its hostile £2.7 billion buyout offer in December.

Furse and the London board have refused to speak with their Nasdaq counterparts and vehemently rebuffed the bid in public, leaving the market wondering whether they were fishing for a higher price — common action in a hostile deal — or running scared.

Neither may be the case. In December, Furse told advisors that her best- case outlook would be to fend off Nasdaq, then use fear of the long arm of U.S. regulation to market the London exchange to new customers, after Euronext and the New York Stock Exchange agreed to pair up this year, according to a person briefed on the talks.

Whether Furse can hold off its hedge fund investors, who are putting pressure on the London exchange to cut a deal with Nasdaq, is unclear. Nasdaq, which already owns 28.8 percent of the London exchange, needs a simple majority, or just over 50 percent, to take control. Short-term investors, including hedge funds and the corporate raider Samuel Heyman, own an estimated 30 percent of the stock and will be instrumental in any deal.

Regulatory creep is a big worry for investors and public company executives as trans-Atlantic alliances create more global markets.

The NYSE chief executive, John Thain, has pledged that U.S. regulators will regulate only within American borders after the merger with Euronext, and that the pan-European exchange will keep its French and Dutch regulators. But many European investors are skeptical.

No matter what Americans say, some argue that the reach of the Sarbanes- Oxley law on corporate governance could create a situation where directors and company executives who list on any exchange allied with an American one are liable to lawsuits or tough U.S. rules that provide for prison sentences.

The London exchange has been a big draw in recent years for emerging-market players, who have been scared off from U.S. markets. Thain has been pressing for changes to Sarbanes-Oxley rules.

IHT: London Stock Exchange to buy back shares to fend off Nasdaq