U.S. stocks weakened on Tuesday as disappointing sales from Johnson & Johnson stirred jitters about the strength of earnings, threatening to break the S&P 500's six-day winning streak.

With the last two quarters characterized by cost cutting and layoffs, investors have been optimistic companies may begin to show real revenue growth in third-quarter results or improved outlooks. After a recent rally, investors have grown cautious as the earnings season picks up pace.

If the guidance is good, we can probably survive another anemic topline growth quarter from most of the major companies, said Alan Lancz, president at Alan B. Lancz & Associates Inc in Toledo, Ohio.

Investors will still have something to hang their hat on in that maybe some of the topline growth will come next quarter.

Financial shares led the way down with several major banks reporting results this week. Goldman Sachs Group Inc fell 1.9 percent to $186.48 after influential banking analyst Meredith Whitney downgraded the stock, saying the upside could be limited for the financial services company in the medium term.

Johnson & Johnson beat Wall Street's earnings expectations but reported revenue that came in below forecasts. Shares of the diversified healthcare company fell 2.2 percent to $61.14.

Revenue growth is the key thing this earning season, as it would confirm the economy is growing, said John Canally, investment strategist and economist for LPL Financial in Boston.

The Dow Jones industrial average <.DJI> slipped 18.07 points, or 0.18 percent, to 9,867.73. The Standard & Poor's 500 Index <.SPX> was off 3.38 points, or 0.31 percent, to 1,072.81. The Nasdaq Composite Index <.IXIC> edged down 1.52 points, or 0.07 percent, at 2,137.62.

The Nasdaq's losses were limited after Cisco Systems Inc agreed to buy Starent Networks Corp for $2.9 billion, or $35 per share. Cisco added 0.3 percent to $23.85, while Starent, which makes telecommunications equipment, spiked 16.7 percent higher to $33.89.

Healthcare stocks slid as sweeping U.S. healthcare reform was poised to clear a key Senate hurdle with the backing of influential Republican Olympia Snowe.

The Morgan Stanley Healthcare Payor index <.HMO> fell 2.4 percent. Investors have fretted about what a potential healthcare overhaul would mean for the profits of health insurers.

Key earnings due after the close included Intel Corp , while JPMorgan Chase & Co , Citigroup Inc , Goldman Sachs and Bank of America all report throughout the week.

(Additional reporting by Ryan Vlastelica; Editing by Kenneth Barry)