US STOCKS-Wall St pulled lower by semis, financials

* Morgan Stanley downgrades semis, Intel falls

* UBS posts loss; RBS, Lloyds agree to shake-up

* Berkshire bid for Burlington Northern boosts industrials

* Dow off 0.7 pct, S&P off 0.6 pct, Nasdaq off 0.7 pct

* For up-to-the-minute market news, click [STXNEWS/US]

(Updates to midday, changes byline)

By Leah Schnurr

NEW YORK, Nov 3 (Reuters) - U.S. stocks stumbled on Tuesday after Morgan Stanley downgraded the semiconductor sector and a shake-up at two big British banks prompted investors to sell financial shares.

Losses were limited as Warren Buffett's Berkshire Hathaway agreed to buy Burlington Northern in a deal that values the railroad company at $34 billion. Burlington shares surged 28.3 percent to $97.59, boosting the industrial sector nearly 1 percent. For details see [ID:nN03483590].