In a fitting end to a frenzied week, U.S. stock prices gyrated wildly yesterday before limping to a close with major indexes flat to slightly lower.

The Dow Jones industrial average ended the day with a loss of 31.14 points, at 13,239.54, after coming tantalizingly close to being up.

The Standard & Poor’s crossed the finish line up 0.55 at 1,453.64, while the Nasdaq composite index declined 11.60 points to 2,544.89.

But as few would have predicted yesterday, all three major benchmarks wrapped up a week of often surreal volatility with net gains.

The hero riding to the rescue? The Federal Reserve, which, along with other central banks around the world, injected more cash into global markets.

“At least for this week, we feel that we have priced in the worst-case scenario,” said Art Hogan, market strategist at Jefferies & Co.

However, rumors and fears continue to swirl throughout Wall Street, raising anxiety about what could happen after the opening bell rings Monday.

“We have moved from worrying about the extent of real problems in the subprime lending arena to questions about which hedge funds are down and how much,” said Jeff Rubin, a market analyst at Birinyi Associates.

The concerted central bank action helped reverse the sell-off, traders and investors agree.

“They’re telling us that they’ll be there to be sure that there is going to be liquidity, that they’re not going to let liquidity just dry up,” said one trader.

That vigilance is reassuring.

“The Fed hasn’t eased, but they are standing by and are vigilant,” said Jason Trennert, a partner at Strategas, a market research firm.