* Higher Procter & Gamble outlook reassures on consumers
* Data spurs optimism about economy
* Monsanto tumbles as 2010 forecast below Street views
* Dow up 0.8 pct, S&P up 1 pct, Nasdaq up 1.2 pct (Updates to close)
By Angela Moon
NEW YORK, Sept 10 (Reuters) - U.S. stocks gained for a fifth straight session on Thursday, their longest string of gains since November, as a bright outlook from consumer product company Procter & Gamble and a successful Treasury bond auction boosted investors' confidence.
Strong demand for the sale of 30-year Treasury bonds lifted confidence in U.S. assets, including stocks. The S&P 500 stock index rose to its highest in nearly a year.
Procter & Gamble was the Dow's biggest lift, climbing 4.2 percent to $56.04 after it affirmed its earnings forecast for the current quarter and said sales would improve in the next quarter.
"There is no selling pressure in this market. You see more believers in the market, more bullish sentiment and people are starting to believe that this rally is real," said Keith W. Springer, president at Capital Financial Advisory Services in Sacramento, California.
The S&P now stands 54 percent higher from its 12-year closing low on March 9.
Chip companies Texas Instruments and ASML both boosted their sales outlooks in a signal consumers are spending cash on personal technology. Semiconductor shares gained 1.8 percent.
The Dow Jones industrial average was up 80.26 points, or 0.84 percent, at 9,627.48. The Standard & Poor's 500 Index gained 10.77 points, or 1.04 percent, at 1,044.14. The Nasdaq Composite Index was up 23.63 points, or 1.15 percent, at 2,084.02.
Adding to optimism was jobless claims data, which fell to its lowest since July last week, while a separate government report showed imports of foreign goods rose to a record, suggesting more strength in U.S. consumer spending.
But among decliners, Monsanto, the world's biggest seed company, fell 5 percent to $79.30 after it forecast fiscal 2010 earnings below Wall Street's estimates.
Health insurance stocks rose 3.5 percent after analysts said President Barack Obama's speech urging Congress to act on health care reform indicated a government-run insurance option opposed by the industry was less likely to pass.
On the Nasdaq, Yahoo Inc added 4.5 percent to $15.45 after Banc of America Securities-Merrill Lynch Research upgraded the company, saying growth in user traffic continues to outpace growth in the Internet as a whole.
An airlines stocks index added 6.7 percent after J.P. Morgan said fundamentals for the U.S. airlines sector are on the mend and upgraded UAL Corp and U.S. Airways Group Inc.
UAL Corp, United Airlines parent, jumped 17.8 percent to $7.60 while U.S. Airways shares surged 12.3 percent to $4.02.
Volume was moderate on the New York Stock Exchange where 1.49 billion shares exchanged hands, in line with last year's estimated daily average of 1.49 billion.
On the Nasdaq about 2.45 billion shares traded, above last year's daily average of 2.28 billion.
Advancing stocks outnumbered declining ones on the NYSE by a ratio of about 23 to 7. On the Nasdaq, about 17 stocks rose for every eight that fell. (Editing by Kenneth Barry)