PARIS, Sept. 29 - Mayor Michael R. Bloomberg, on his first trip here since he took office, acknowledged the challenges of bringing home a popular Parisian bike rental program the administration is exploring, saying he was unsure it would translate to New York.

Noting challenges like roads damaged by seasonal changes, the lack of bike lanes, liability problems and the possibility that commuters would not want to carry helmets to work, Mr. Bloomberg said: "You try to see whether it fits, and some parts of it will, but it may very well give you an idea to do something totally different."

Under the program, which started in July, thousands of bicycles are docked along Paris streets, and customers can rent them after buying a membership ranging in time from a day (about $1.30) to a year (about $38). Members pay by the half-hour, with the first 30 minutes free. To discourage long rides, the fee rises from $1.30 for the second half-hour to $5.20 for the fourth.

Judging from the lines of empty consoles in the city center and the ubiquity of riders, even in the rain, the program has been a hit here, despite occasional technical glitches and a lack in some places of empty spots to return a bicycle. One official told Mr. Bloomberg that 100,000 people had signed up for yearly membership and that customers had taken more than 5 million rides.

Whether such a system could survive in New York, where bike theft is common, remains to be seen. Lionel Bordeaux, a press officer for City Hall here, said the fact that all fees were paid by credit card, and a roughly $200 charge for unreturned bikes, discouraged stealing.