NEW YORK - THE S&P 500 and Nasdaq rose slightly on Tuesday as news of a major railroad acquisition helped sentiment, but the Dow edged lower on caution before a Federal Reserve statement on interest rates and the economy.

Morgan Stanley's downgrade of semiconductor stocks also limited a broad advance.

The Dow Jones Transportation Average rose 5.3 per cent as Warren Buffett's Berkshire Hathaway agreed to buy Burlington Northern Santa Fe Corp in a deal that values the railroad company at US$34 billion (S$47.6 nillion), Berkshire's biggest deal ever. Burlington shares jumped 27.5 per cent to US$97.

'One of the themes we've been pointing toward is that the next catalyst after earnings is M&A activity, and we've had some big ones,' said Tim Smalls, head of U.S. stock trading at brokerage firm Execution LLC in Greenwich, Connecticut. 'People consider companies to be cheap.'

The Federal Open Market Committee began a two-day meeting on Tuesday. While investors expect the Fed to leave rates close to zero, they are nervous to hear what the officials say about the economic outlook.

The Dow Jones industrial average slipped 17.53 points, or 0.18 per cent, to end at 9,771.91. But the Standard & Poor's 500 Index added 2.53 points, or 0.24 percent, to finish at 1,045.41. The Nasdaq Composite Index advanced 8.12 points, or 0.40 percent, to close at 2,057.32. -- REUTERS