New York starts clean up efforts after hurricane
* 38,000 New York customers without power
* Mayor Bloomberg says "big cleanup" effort ahead
* Subways reopen, some commuter rail lines still suspended
* U.S. financial markets up and running
NEW YORK, Aug 29 (Reuters) - New Yorkers returned to work under blue skies on Monday but the destruction left by Hurricane Irene made commuting a nightmare for thousands in the city's suburbs whose train service was suspended by flooded or blocked rail lines.
The storm's strong winds and heavy rains downed some 2,000 trees on Sunday, leaving branches and debris scattered across streets and thousands of residents without power.
"We have a big cleanup job ahead of us, no question about that," Mayor Michael Bloomberg said at a press conference.
He said about 38,000 New York City customers remained without power, but added he hoped electricity would be returned within a day or two.
Subway service resumed at 6 a.m. on Monday, after officials shut it down at noon on Saturday in preparation for the storm. The city's bus service was also running normally on a morning when New York enjoyed a spell of dry, warm weather.
Commuters from New Jersey, Connecticut and Long Island had a more difficult time of it, with many unable to get to their jobs in Manhattan because of train cancellations due to flooded stations and tracks and damage from fallen trees. Some turned to buses, ferries or car pools, while others worked from home or took the day off.
At Pennsylvania Station, a picture of the flooded Trenton, New Jersey, train station was hung in the window of the Amtrak teller booths to show customers why trains had been canceled.
Across town, a clerk at Grand Central Station was advising Metro North commuters that there would likely be no service to Connecticut on Monday, and that there was no guarantee trains would be running on Tuesday.
Peter Rugen, 45, a banker who normally commutes to work in Stamford, Connecticut, from his home in Manhattan, was frustrated there would be no trains Monday.
"I'll probably just pay a taxi a lot of money to take me there," he said, adding it would cost about $120, compared to the train fare of $12.25.
FINANCIAL MARKETS OPEN
Irene weakened before it struck New York on Sunday and damage was less severe than feared in low-lying areas of the city, particularly in downtown Manhattan's financial district.
About 370,000 people across the city were evacuated ahead of the storm and officials feared windows in skyscrapers would shatter and subway tunnels would flood.
But with the city largely spared, financial markets opened as normal on Monday, with the New York Stock Exchange, the Nasdaq Stock Market and the alternative BATS venue starting the week as usual.
The doors of the New York Stock Exchange had been lined with sandbags and tarps on Sunday in anticipation of a flood but they were were nowhere to be seen on Monday morning.
Federal courts in New York were also open, while air travel at major airports slowly started to resume service.
With donors unable to give blood over the weekend, the New York Blood Center said its supplies had run low and it put out an emergency appeal for donations.
The National Tennis Center in the borough of Queens escaped serious damage and the U.S. Open was due to start on Monday as scheduled.
A football game between the New York Giants and New York Jets was also due to go ahead on Monday evening at the Meadowlands stadium in New Jersey, despite forecasts that flooding in the state could get worse in the coming days.
Bloomberg said the economic impact would likely be a "mixed bag" for the city's 8.5 million residents and its businesses, since sales of emergency items such as batteries, flashlights and water would help offset lost sales at stores closed Sunday by the storm.
"In the grand scheme of things, it isn't something that most people can't survive through." (Reporting by Reuters bureaus throughout the East Coast; Editing by Eric Beech)