(Adds additional comment from Hartford, closing share activity)

NEW YORK, Oct 2 (Reuters) - Insurance stocks, led by Hartford Financial (HIG.N: Quote, Profile, Research), Principal Financial (PFG.N: Quote, Profile, Research) and MetLife (MET.N: Quote, Profile, Research), fell on Thursday, a day after a top lawmaker raised the question of whether a well-known insurer could be in financial trouble.

Wall Street is already worried insurers will be hurt by investment losses and exposure to recent corporate collapses, including American International Group Inc, Lehman Brothers Holdings Inc and Washington Mutual Inc as well as commercial and residential real estate debt.

U.S. Senate Majority Leader Harry Reid, a Nevada Democrat, said it was imperative that the $700 billion financial bailout plan get legislative approval, adding that a well-known insurer's solvency could be threatened if financial markets remained volatile.

Reid, speaking to reporters Wednesday, did not name the insurer. A spokesman said Thursday the comments were not directed at any particular company.

"His comments were meant to refer to the conditions in the financial sector generally. He regrets any confusion his comments may have caused," said spokesman Jim Manley.

Nevertheless, all but two of the stocks in the S&P Insurance Index fell Thursday, sending the index down 8 percent.

Hartford Financial Services Group Inc, a large life and property insurer, lost 32 percent, its worst one-day percentage drop since at least December 1995.

Principal Financial Group Inc, a large life and health insurer, and MetLife Inc, the largest U.S. life insurer, also fell sharply, closing down 16.3 percent and 15 percent, respectively. Prudential Financial Inc (PRU.N: Quote, Profile, Research), the No. 2 U.S. life insurer, dropped 11 percent.