Along with the budding trees, chirping birds, and backyard barbecues, the roaring debate has returned this spring in New Hampshire over where dirt bikes and all-terrain vehicles should be able to kick up some dirt and zoom around.

The debate could be the loudest yet between homeowners who don't like the dust, noise, and land damage created by the motorized machines, and riders who say there are not enough trails in New Hampshire or neighboring Massachusetts to enjoy the ever-growing sport. So far, riders of dirt bikes and all-terrain vehicles appear to be losing ground. Towns such as Kingston and Windham have taken steps this year to restrict, either permanently or temporarily, dirt bikes and ATVs on town-owned property, while Merrimack is considering bans on two parcels of land. At the same time, homeowners and environmentalists have stalled plans for the state to expand its trail system to private property in Mont Vernon and Lyndeborough, and to Bear Brook State Park in Allenstown. "It's just so tough to enjoy something like this. There are fewer and fewer places to go. It's kind of frustrating," said Jim Picariello, a 47-year-old engineer from Danvers, Mass., who drove to an old train depot in Windham on Sunday to go four-wheeling with his 16-year-old son, Josh, on a 17-mile state-owned trail. "People [who oppose this] don't understand the father and son bonding that goes on. It's such an enjoyment."

Opponents, such as Mark Samsel who lives in a Colonial house next to the Windham train depot, don't necessarily object to the ATV riding, but think it should take place somewhere away from populated areas where trails are increasingly running behind new housing developments. "Not in this area. It doesn't make sense," said Samsel, a 46-year-old director of a software company, who criticizes the state for wanting to add more trails in southern New Hampshire. "If I buy a 35-foot boat, do I ask to dredge [nearby] Massabesic lake so I can get my boat in? No. . . . I'm going to Newburyport or Lake Winnipesaukee." Opponents and proponents of ATVs and dirt bikes are closely watching two disputes in southern New Hampshire that could have far-reaching implications in how the state resolves such controversies and how it might be able to expand its trail system to accommodate a growing number of users. About 27,500 riders of dirt bikes and ATVs have registered with the state this year and will use about 500 miles of state-run trails - an amount that motorized sports enthusiasts say is too small.

In the first dispute, the state Senate is considering legislation, already approved by the House, that would ban parking at the old train depot in Windham between dusk and dawn and would forbid riding motorized vehicles on a stretch of Rockingham Trail west of Route 28, unless it is covered with snow. The legislation aims to curb the amount of noise, dust, and litter created by ATV users. Such changes, however, are typically approved by the commissioner of the state Department of Resources and Economic Development, which oversees the state trail system, but ATV opponents generally fault the agency for being biased toward ATVs. If the legislation passes and is signed by the governor, it could clear the way for similar disputes to be resolved by the Legislature.

The second dispute is a lawsuit that tests the power and scope of a law passed last year giving the Department of Resources and Economic Development the power to expand the state trail system without receiving local approval, according to the attorney general's office. The intent of the law, the state contends, was to prevent the so-called "not-in-my-backyard" syndrome from blocking expansion of the state trail system.

Lyndeborough, a town of 1,500 west of Nashua, is suing Barbara Boisvert and her son, Larry, who offered the state free use of their 850 acres in that town and neighboring Mont Vernon, after failing to receive local approval for a commercial recreation park. A Hillsborough County Superior Court judge is expected to make a ruling in the case sometime this spring or summer.

"Everywhere you turn around, people have problems with these things," said David Romer, a Lyndeborough resident whose property abuts the proposed ATV trails. "Hopefully, the public outcry will get loud, and hopefully people in Concord will take notice." ATV and dirt bike enthusiasts blame the opposition to them on a few "bad apples," including some unsupervised teenagers, who anger neighbors by violating rules and on the state for failing to provide enough trails, which makes the 500 miles of legal trails crowded, noisy, and dusty.

"This thing of a 15-year-old riding an ATV as a baby-sitting machine is real, but that's not the majority of us," said Richard Gourdarzi, executive director of the Granite State ATV Association. More upsetting to Gourdarzi is how motor sports enthusiasts are being demonized. At state hearings, he said he heard opponents compare ATVs to "weapons of mass destruction" and "biohazards." "We're really up against the negative hype in the last 10 or 15 years," said Gourdarzi, who pointed out that his group never gets publicity for doing good deeds such as raising money for cystic fibrosis research or Toys for Tots, or volunteering to patrol the trails to make sure garbage is picked up and riders obey the rules.