On a sweltering August afternoon, George Watson wedged himself, his briefcase and his bundled-up sports jacket and raincoat into a narrow seat aboard the profoundly un-air-conditioned No. 38 bus rumbling east down High Holborn in London's bustling city center.

Steam seemed to rise from the pavement, and beads of sweat attacked his forehead, cheeks and graying mustache, but Watson, a mass transit consultant, didn't seem to notice. He was singing the praises of the Routemaster, the vintage 1950s double-decker model that plies the 38 and a dozen other major London bus routes -- its maneuverability, its seating arrangement, its smooth braking system, but most of all, its rear platform that allows passengers to hop on and off freely.

"What we have here is an icon of London," Watson declared. "It's fast and efficient, with a conductor and seats and on-and-off flexibility. How could anyone fail to appreciate this vehicle?"

These days not everyone does. The people in charge of Transport for London, the agency that operates the city's sprawling and rapidly growing bus network, have decreed that it's time for the 50-year-old Routemaster to go. It's already been replaced by other types of buses on half its 30-odd routes, and by sometime next year, just one "heritage route," as the agency calls it, will be left as a salute to the past.

Old age and expense have conspired to make the Routemaster obsolete, its critics contend. But the chief culprit is the feature that Watson and other aficionados most admire: the distinctive rear platform. It doesn't meet modern standards for safety and accessibility for the disabled, Transport for London argues -- two to three people die each year falling off a platform -- and it requires that each bus be staffed by a conductor as well as a driver.

Red double-decker buses will remain a fixture on London's streets, officials insist, but with standard doors for entry and exit -- no more rear platform and, therefore, no more Routemaster.

"We all love the Routemaster," said Graham Goodwin, a spokesman for Transport for London. "But you can't ask people to produce a modern bus service and tie one hand behind their back. It's a sad fact of life. I love my old typewriter, too, but at work, I use a computer."

This being London -- a city that reveres tradition even as it slouches into the 21st century -- the Routemaster is not going without a fight. A grass-roots Save Our Routemaster campaign has collected more than 5,000 signatures, and the Evening Standard newspaper and LBC Radio have taken up the cause. A few weeks back, supporters held a rally at which 100 of the lumbering old beasts made a proud appearance.

"It's not over until the last bell dings," said Benedict Brook, head of the all-volunteer campaign.

Most tourists and many Londoners don't know a Routemaster from any other double-decker -- but they do know its distinctive rear platform, which has helped make the bus as much a symbol of London and England as black taxis and red telephone booths. Killing it off for the sake of modernity would be like putting a digital face on Big Ben, Brook says.

Critics also express disbelief that London is about to trade an elegant, British-designed vehicle for modern articulated buses and double-deckers built by the likes of DaimlerChrysler and Volvo in exotic countries like Germany and Sweden. The newcomers, sniffed Jonathan Glancey, architecture critic for the Guardian, are little more than "loud, overweight, gas-guzzling, driver-only mobile shoeboxes."

In a recent column, Glancey said the newer models suffer from "muddled floorplans, decor designed as if by an underachieving ape let loose with a box of crayons, an ear-splitting engine, hissing air-brakes, sticky, plastic-backed seats, some facing backwards to induce nausea, and lighting swiped from an FBI interrogation room."

The battle over the Routemaster is taking place at a time when London bus travel has undergone a remarkable resurgence. Ridership has reached nearly 6 million a day -- an increase of more than 40 percent in just three years, and double the number of passengers who travel daily on the Underground, London's famed rail system.

Experts cite several reasons: Bus service has improved in recent years, with more lines and 1,000 new vehicles, while the price has remained stable -- the equivalent of about $1.15 a ride for those who buy a six-ticket pack. London's "congestion charge" -- the $9 fee collected from private motorists who drive into the city center during weekday business hours -- has been another factor, as has the Underground's reputation for unreliability.

Still, says David Begg, chairman of the Commission for Integrated Transport, a government-funded research and advisory group, the big jump in bus usage has taken many experts by surprise. "The conventional view was you couldn't get people out of their cars and into buses, but the London experience has proved it wrong," he said.

Transport for London spends about $1.8 billion a year on buses and receives about $1.3 billion in passenger fares; the rest is subsidized by taxes. Money is tight, and Goodwin, the group's spokesman, estimates that the Routemaster costs 10 to 15 percent more to operate than its modern successors because it requires a two-person crew and can accommodate only 77 passengers -- as opposed to 88 on a more modern double-decker and 129 on an articulated single-deck vehicle.

To show off the charms of the newer models, Transport for London recently invited a handful of journalists to the Millbrook Proving Ground, north of the city, to test-drive the Routemaster and two of its successors, the modern double-decker and the articulated vehicle known here as a bendy bus.

The modern models had about twice the engine power of the Routemaster. Power steering and automatic gearboxes made them as easy to drive as an overgrown sports utility vehicle, while the Routemaster's steering wheel required strength and commitment.

Even entering the vehicles provided a marked contrast: The driver gets into the modern models by opening a gate inside the bus, while a Routemaster driver has to pull himself up by two handles on the outside of the vehicle and climb through the side window.

Still, there was something intangibly thrilling about the older model. "It's a grand old bus, and it's fun to drive," said Bill Todd, 42, an instructor assigned to supervise the Routemaster test drive. When it comes to the gas pedal and the steering wheel, he said, "you've got to feed it in and feed it out. You know you're driving it all the time."

There's one other feature of the Routemaster that aficionados worship: its seats. The bus was designed to let a maximum number of passengers get off their feet -- 72 in all. Although its successors hold more people, they have fewer seats because more space is taken up for wheelchairs, baby strollers and other conveyances.

"The Londoner's got no choice," said Watson, the transit consultant. "Deprive him of his seat and he's got to stand. Ask the average rider and he'll prefer the Routemaster anytime."

Not every passenger on the 38 agreed. Tanya Mowat, 25, an online travel service employee who moved to London from New Zealand three months ago, said she was unaware she was riding a Routemaster. "One way or the other, they're all double-deckers," she said. "When I call my nieces back home and I tell them I'm riding a double-decker, they get very excited."

But Frank McShane, 64, a committee clerk at the House of Commons, said he knew the difference. "I've always liked this bus because you can get on and off freely," he said. "There are more seats and less standing. It's a great British tradition and a very sensible method of travel. It will be a shame to see them go."

Fans look over a line of Routemasters at a recent 50th anniversary celebration. A grass-roots campaign is trying to keep the buses on London streets. The Routemaster is known for its rear platform, which lets riders hop on and off at will. Transit officials say the exit does not meet modern safety standards.