Marc Smoot is 37, but he feels like a kid again when he rushes down dirt trails on his mountain bike. He especially enjoys the sound of crickets and smell of flowers when he rides at night, guided by a bicycle lamp as powerful as a car headlight.

Smoot is among hundreds of cycling enthusiasts attracted to the Palos Verdes Peninsula's hilly terrain and freedom of its open spaces.

While Smoot says he is always courteous to other trail users, a small number of bikers have failed to follow his lead.

On the road, cyclists traveling in packs as large as 80 sometimes hold up cars and flout traffic laws. And off the road, mountain bikers occasionally clash with hikers or spook horses and their riders.

In the past month, officials in two of four peninsula cities have discussed ways to keep mountain bikes off horse trails, and another city says complaints regarding mountain bikes are increasing.

"There are some (mountain bikers) that are considerate, and some that barrel over those hills," says Palos Verdes Estates resident Georgeann Dorn, who sent a letter to City Hall complaining about reckless mountain bikers after her husband narrowly escaped being run over twice.

Palos Verdes Estates City Hall, which had never had any complaints about mountain bikes before, has received about half a dozen over the past few months, said Scotty Steiner, secretary to the City Council and the city manager.

In Rolling Hills Estates, the equestrian committee also received a complaint last month.

In nearby Rolling Hills, where mountain bikes are banned from horse trails, Councilman Godfrey Pernell said at a recent council meeting that he spotted bikers near the gated city's trails, and City Manager Craig R. Nealis promised to notify Los Angeles County sheriff's deputies.

Deputies patrol three of four peninsula cities, and say they have not received any formal complaints, but if mountain biking became a major issue, they could deploy horse, motorcycle or mountain-bike patrols.

The mountain bike, known for its thick frame and wide tires, has grown in popularity over the past several years. But in Rolling Hills Estates, an ordinance banning all bicycles from the city's 30 miles of horse trails dates to 1979, said City Manager Doug Prichard. Rolling Hills' ordinance dates to 1990, said City Manager Nealis.

Violating the ordinances is a misdemeanor, punishable by a $1,000 fine and up to six months in jail. But, officials say the ordinances have rarely, if ever, been enforced.