"It'll be nice not to have it sitting out there in the trash," Ms. Murphy said. "That's the main reason we're doing it: to improve the odor of Portland."

Just when their infant girl is due to arrive, Portland will be experiencing its first summer of biweekly garbage pickup. The change to every other week, introduced in cool weather last fall along with a weekly collection for food scraps, has reduced the amount of garbage that this progressive city is shipping to landfills by 44 percent.

The experience has not been entirely smooth. Since the garbage pickups were spaced out, the city's main recycling company has complained that more garbage — disposable diapers included — is showing up in recycling bins. Residents complain about strong smells from garbage that has stewed for two weeks in the driveway.

Yet while some grumble, many say the inconveniences, and occasional startling whiff, are prices they are willing to pay to live on the leading edge of recycling.

"It was fuller and stinkier, but for the overall sake of the mission, we were willing to deal," Penelope Miller, a resident with a 2-year-old daughter, said of her trash can.

Pioneers like Portland, Seattle and San Francisco have become so good at waste diversion that it is becoming harder to get much better. San Francisco reuses a whopping 78 percent of what enters its waste stream, compared with the national average of 34 percent.

As some press toward a goal of "zero waste," the challenge is asking residents to conquer what officials call "the ick factor" of organic waste, endure fewer garbage pickups, become more sophisticated sorters and live without things like plastic grocery bags and polystyrene containers for their takeout food.

At the same time, the cities are exploring novel solutions for recycling challenging materials that take up relatively far more space at the dump than they did before recycling took hold. Those targets include construction debris from small haulers, complex plastics, polystyrene foam and the smelliest of the smelly: cat litter, dog poop and diapers.

"We have the infrastructure in place that could theoretically take us to 85 percent," said David Assmann, the deputy director of San Francisco's Department of the Environment. "The challenge is going to be that last 15 percent. We don't have a blueprint yet that says exactly how we're going to get to zero."

The march to this moment has taken more than three decades. It began with newspaper and cardboard recycling in the 1970s; expanded to glass, aluminum, plastics and other materials; and is now conquering the last relatively easy-to-divert target: food scraps and yard debris that can be turned into compost. In some cases, the compost it creates is sold or given right back to the residents who threw it out.

The West Coast became a leader in part because it has easier access to markets in Asia that buy recyclable materials like paper and plastic. It also has significantly higher landfill costs than many other regions.

The leading cities have long traditions of environmental progressivism and are relatively small, with 800,000 or fewer residents apiece. Portland and Seattle in particular have many single-family houses, where the most responsible recycling takes place.

This summer, Seattle is opening a mammoth new transfer station in an industrial area south of downtown. With a far larger floor area, it will be able to sort waste more thoroughly, including construction debris.

The building puts a bright face on what some people might otherwise deem a dirty industrial endeavor. Old street signs decorate its entrance, a former drawbridge is a sculpture out front, the landscaping is irrigated with captured rainwater, and waste is misted to keep odors down. Windows allow abundant natural light.

"People who have had a hard time finding their transfer station aren't going to have a hard time now," said Juwan Williams, a scale attendant for 18 years at the gritty old South Transfer Station. "You can see this place from space."

Seattle requires composting as well as recycling. Dick's Drive-In, a beloved local burger chain that has been around since 1954, provides multiple bins with photographs clarifying for customers which piece of waste goes where.

"A shake is all three," said Eli Hays, who works at the restaurant's Wallingford neighborhood location. "The lid is recyclable, the straw is garbage, and the cup is compostable."

Not everyone supports the mandates.

Chris Baldwin, a Dick's regular, said he had "issues with being told I have to recycle." Turning to three colleagues who had joined him for a late lunch spread across the bed of a pickup truck, he said, "We wait until Seattle police go by, and we throw it all in the garbage."

Next month, Seattle will begin a pilot program for biweekly garbage pickup. By 2018, it wants to provide some neighborhoods with a fourth curbside bin for diapers and pet waste. The feces would be placed in anaerobic digesters to produce power.

"It doesn't look any weirder now than collecting food waste looked weird to us 12 years ago," said Tim Croll, the head of the solid waste division of Seattle Public Utilities.

Still, there are aggravations for trash handlers.

In Portland, the move to collecting food scraps added to a problem with sea gulls at one of the city's main transfer stations. In January, a falconer was hired to patrol the site with three falcons to deter the gulls.

"When we started, there were about 400 birds," said the falconer, Kort Clayton. "Today, the average is less than a few each day."

Mr. Clayton noted that the gulls had easy pickings in the piles of food scraps but flocked to the garbage as well — evidence that some residents and businesses are not separating their waste. "There's still food in the garbage," he said.

And the week after Portland switched to biweekly garbage collection on Oct. 31, Far West Fibers, which handles more than 70 percent of the city's recyclables sorting, saw a 50 percent increase in the amount of garbage in the weekly recycling loads, said the company's president, Keith Ristau.

While dirty diapers make up only a small amount of the contamination, he said, "that doesn't make it any less disgusting" for workers at the recycling plant.

"They have to stop the line and pull the diaper off," Mr. Ristau said. "You can't really grab it when it's going 150 feet a minute on the conveyor belt."

For Joe Gatto, a driver for Portland Disposal and Recycling for the past 13 years, the new nemesis on his biweekly garbage route is the steep rise in cat litter.

"It smells really bad," he said. "And you get the added negative that it's really heavy."