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* Obama to seek congressional authorization for Syria action
* Verizon and Microsoft fall after announcing major deals
* ISM Manufacturing index comes in ahead of expectations
* Indexes: Dow off 0.05 pct, S&P up 0.27 pct, Nasdaq up 0.48pct
By Chuck Mikolajczak
NEW YORK, Sept 3 (Reuters) - U.S. stocks advanced modestlyon Tuesday as an early rally faded after two top Republicansvoiced support for U.S. President Barack Obama's call forlimited strikes against Syria.
Both the S&P 500 and Nasdaq rallied to the tune of more than1 percent in the early stages of trading after Obama decided toseek congressional authorization before taking military action,a move likely to shelve any strike for at least several days.
Both John Boehner, the Republican speaker of the U.S. Houseof Representatives, and Eric Cantor, the House Republicanmajority leader, pledged support for military action in Syriaafter a meeting on Tuesday at the White House. Boehner urged hiscolleagues in Congress to do the same.
Nancy Pelosi, Democratic leader in the House ofRepresentatives, said she believes Congress will support aresolution authorizing the use of U.S. military force againstSyria.
"The worry is Syria could turn ugly," said Jeffrey Saut,chief investment strategist at Raymond James Financial in St.Petersburg, Florida.
Equities have recently been pressured by the prospect of aWestern strike against Syria after chemical weapons were used tokill civilians, sending the S&P down 1.8 percent last week anddown 3.1 percent for August.
Congress returns from its summer recess on Sept. 9, and anyvote to authorize a strike will come after that.
U.S. crude futures rose 0.9 percent. Oil spiked 2.5percent in August, largely driven by concerns that militaryaction in the Middle East would disrupt crude supplies.
The Dow Jones industrial average fell 6.86 points or0.05 percent, to 14,803.45, the S&P 500 gained 4.38points or 0.27 percent, to 1,637.35 and the Nasdaq Composite added 17.409 points or 0.48 percent, to 3,607.278.
Verizon Communications agreed on Monday to pay $130billion to buy Vodafone Group out of its U.S.wireless business, ending an often tense 14-year marriage.Verizon lost 2.7 percent to $46.10 while U.S. shares of Vodafoneshed 2.3 percent to $31.61.
Nokia Corp agreed to sell its handset business toMicrosoft Corp for $7.2 billion, sending its U.S.shares up 29.7 percent to $5.06 on record volume. Microsoftfell 5.8 percent to $31.45, the biggest drag on both the Dow andS&P 500.
In the latest economic data, the Institute for SupplyManagement's August manufacturing index came in at 55.7, aboveexpectations for a reading of 54. July construction spendingrose 0.6 percent, twice the rate that had been expected.
In addition, financial data firm Markit said while its finalU.S. Manufacturing Purchasing Managers Index eased to 53.1 fromJuly's reading of 53.7, a pickup in new orders and a drop ininventories pointed to faster growth ahead.
In the S&P, investors were watching the 100-day movingaverage at 1,639.42, which the index has been unable to closeabove since Aug. 26. Holding over that level would be a positivesign of near-term momentum.
CBS Corp on Monday reached an agreement with TimeWarner Cable Inc to end a month-long blackout of itsstations in New York, Los Angeles and Dallas. Financial terms ofthe deal were not disclosed. Shares of CBS rose 4.1 percent to$53.22 while Time Warner Cable added 1.1 percent to $108.58.
