* FTSEurofirst 300 down 0.3 pct, Euro STOXX 50 dips 0.4 pct
* Carnival drops for 2nd day as analysts downgrade rating
* Nordea hit after govt sells remaining stake
By Blaise Robinson
PARIS, Sept 25 European shares dipped early on Wednesday as nagging concerns over a potential U.S. government shutdown at the end of the month and uncertainty about the outlook for the Federal Reserve's stimulus programme kept investors on edge.
Nordic lender Nordea featured among the top losers, sliding 3.1 percent after the Swedish government said it had sold its remaining 7 percent stake in the bank for 76 Swedish crowns per share, a 4 percent discount to Nordea's closing price of 79.2 crowns on Tuesday.
Carnival Corp, the world's largest cruise operator, slumped 5.5 percent, extending the previous day's sell-off as Exane BNP Paribas and UBS downgraded the stock following a 30 percent fall in third-quarter profit reported on Tuesday.
At 0735 GMT, the FTSEurofirst 300 index of top European shares was down 0.3 percent at 1,254.31 points. The index has slipped 1.4 percent since hitting a five-year high last week.
The euro zone's blue-chip Euro STOXX 50 index was down 0.4 percent at 2,912.07 points.
Congressional authorisation for the U.S. government to spend money runs out at the end of the fiscal year on Sept. 30, and a small number of Tea Party-backed U.S. senators have been threatening to stall a bill to renew the funding.
Investors have also been fretting about next month's negotiations in Washington to raise the federal debt ceiling to prevent a default.
"Investors are still confused about the Fed's monetary policy, and now the focus is switching to negotiations between Democrats and Republicans in Washington. After such a rally, people are now very cautious," said Guillaume Dumans, co-head of research firm 2Bremans.
European stocks have rallied since late June, boosted in part by data showing the euro zone is crawling out of recession.
Despite the dip seen in the past week, the broad STOXX Europe 600 is still up 5 percent so far this month, on track to post its best monthly performance in two years, and its best month of September since 1997.