Bicyclists made good time rolling into work over the Queensboro Bridge yesterday, but many face a tough choice: risk leaving it outside, or leave it home.

The transit strike has forced thousands of commuters to cycle to work - but many office buildings bar riders from bringing their bikes inside.

The ban has forced bikers to lock up outside - and risk having their two-wheeled rides stolen.

"I have not ridden my bike to work," said Cheryl Cook. "I was told that under no circumstances can I bring my bike into the building."

Cook, who lives in the East Village, said that because the Eighth Ave. building where she works won't allow bikes inside, she's been forced to take a $10 cab ride to Chelsea since the strike began.

The problem is not a new one for many city cyclists - but it has affected thousands more commuters since the strike began because they have been turned into cyclists by necessity, said transportation advocates.

Before city transit workers walked off the job, an estimated 40,000 New Yorkers pedaled to work each day, according to the advocacy group Transportation Alternatives.

Since the strike began, the group estimates, 200,000 commuters are biking to work.

"At the very least, under these very stressful circumstances, buildings could be more courteous and let their tenants come inside with their bicycles," said Transportation Alternatives spokesman Noah Budnick. "People need to get to work."

Predicting a big increase in bike commuters, some building managers said they have found space to store bikes inside their buildings since the strike began.

"They're trying to make accommodations," said Cheryl Mitchell, spokeswoman for the Building Owners & Managers Association of Greater New York, Inc.

Mitchell said building managers don't normally allow bikes in because of fire code and liability concerns and because the vehicles are disruptive to the heavy traffic flow in their elevators.

"I like my bike; I don't want to get it stolen," said Brett Berkowitz, an engineer who works in lower Manhattan. Berkowitz said he'd rather spend $15 on cabs to and from work than jeopardize his bike.

Berkowitz said a manager at 88 Pine St. where he works said he could not bring his bike inside - even during the strike. Building officials could not be reached for comment yesterday.

A bill that would require office buildings to permit bikes inside has languished in the City Council for two years due to opposition from real estate leaders, advocates said.

"Now people see just how useful a bill like this would be," said City Councilman David Yassky (D-Brooklyn Heights), who sponsored the legislation.