S&P 500 buybacks fall for a fifth straight quarter in Q1

* S&P 500 stock buybacks down 73 pct in Q1

* Buybacks amount to $30.8 billion in Q1

* Buyback seen weak in foreseeable future

NEW YORK, June 18 (Reuters) - Stock buybacks by S&P 500 companies fell for a fifth straight quarter in the first quarter of the year as companies protect their cash flow in uncertain times, said ratings agency Standard & Poor's on Thursday.

Standard & Poor's data show that stock buybacks fell 73 percent in the first quarter compared to a year earlier, and amounted to just $30.8 billion compared to $113.9 billion in the first quarter of 2008. Buybacks are off 82 percent from their peak in the third quarter of 2007 when S&P 500 companies spent $172 billion on buying their own shares.

Repurchasing and canceling shares is a way for companies to return excess cash to shareholders by reducing the number of outstanding shares and therefore boosting earnings per share.

"The need to conserve capital in the current recession, combined with the uncertainty of future cash flow, has made buybacks too high risk for most corporations," said Standard & Poor's senior index analyst Howard Silverblatt in a statement.

The fall in the amount of buybacks would have been even steeper, says Silverblatt, without U.S. oil major Exxon Mobil Corp (XOM.N: Quote, Profile, Research), which accounted for over a quarter of the buybacks in the first quarter. Eighty three of the companies that bought their own shares in the last quarter of 2008 did not do so in the first quarter of this year.

Since the buyback boom began at the end of 2004, S&P 500 companies have spent about $1.8 trillion on stock buybacks compared to $2 trillion on capital expenditures and $1 trillion on dividends. Reported earnings reached $2.3 trillion over the period, according to Standard & Poor's data.

"Standard & Poor's expects buybacks to remain weak for the foreseeable future, even as earnings are expected to improve," said Silverblatt. "The reality appears to be that buybacks as we know them are gone, at least until the return of better times," concludes Silverblatt. (Reporting by Edward Krudy, Editing by Chizu Nomiyama)