NEW YORK (AP) _ Two dozen tiny architects scurried barefoot, sculpting a city from garbage and duct tape. Paper-towel roll trees sprung up around scrap cardboard buildings. Trash-fueled cars sported film-reel tires.

''I just thought it would be pretty,'' said 6-year-old Leopoldine Core, admiring the waterfall she had concocted from shredded computer paper. ''Cities are nice.''

The urban experiment, sponsored by The Children's Museum of Manhattan, was among dozens of displays that opened Eco Expo on Friday, the nation's largest environmental consumer products show.

As children attendees honed their recycling skills, adults staffing 150 exhibits displayed a mix of gee-whiz gadgetry and back-to-basics products, aimed at a public hungry for ideas on how to live in a society free of waste.

Exhibitors peddled purses made from used tires, and invited anyone to flush see-through toilets that purport to cut water use. A scrap yard owner seated on a junked 10-speed bicycle powered a small merry-go-round. An art dealer showed off tiny animal statues created from melted glass and plastic scraps.

A far cry from the glitzy displays found at more high-toned conventions, the frugal exhibits represented a growing class of small entrepreneuers, many of whom were inspired into business by the hubbub around Earth Day 1990, the annual event's 20th anniversary.

The few large exhibitors at the cavernous Jacob Javits Convention Center in Manhattan included General Motors Corp., which displayed a new electric car, and New York's Metropolitan Transity Authority, promoting subway and bus use.

But some visitors expressed skepticism in light of recent reports about corporate exploitation of rising environmental awareness. State officials and activists alike have accused some companies of making misleading claims.

In June, for example, Mobil Corp. paid $150,000 to six states for advertising its Hefty plastic bags as degradable. Mobil withdrew the claim and paid the money without admitting the claim was wrong.

''I have to really go through and review each product,'' said Jim Rohrssen, who made a four-hour trip from Ithaca in hope of finding new ideas to expand his shop of environmentally sound products for kids.

For example, he said, some paper promoted at the show as recycled was actually made of scraps from paper mills. That's been done for years and isn't considered innovative.

While attendance seemed sparse around midday on Friday, show organizers expected around 25,000 people to visit the three-day event.

Other, smaller environmental consumer products shows are held, but Eco Expo, first held earlier this year in Los Angeles and again in Denver, is the biggest.

The event was organized with the environment in mind. Signs exhorting attendees to conserve resources dotted the show. ''In six months, a leaky toilet wastes 45,000 gallons of water,'' read one.

Producer Art Benson said Eco Expo paid the convention supplier an extra $500 to make sure drinks were served in paper cups instead of plastic foam, considered harder to recycle.

Many exposition visitors evidently shared that sensibility.

As children fashioned the trash-layered city in a corner of the convention hall, 11-year-old Kelly Smith was struggling to complete a car - if only someone would give her more duct tape to secure its wheels made of film reels.

''It doesn't use as much, like smoke that comes out of the back of a car,'' she said. Asked how the car would be powered, she said, ''I could use garbage and stuff.''