High-speed-rail executives from around the world gather in Philadelphia this week, hoping to boost support for bullet trains in the United States, where momentum has been slowed by high costs and political disputes.

The Obama administration's pledge to give 80 percent of Americans access to high-speed trains by 2035 seems increasingly unattainable. Instead, attention has shifted to the Northeast Corridor and California, where hopes for 220-mile-per-hour trains remain highest.

"Maybe we can bring a little help to a vision that is perhaps not fully shared yet in the United States," said Jean-Pierre Loubinoux, director-general of the International Union of Railways in Paris and a leader of the Eighth World Congress on High-Speed Rail, which opens here Wednesday.

"The wisest way to proceed is to get it running somewhere."

That could be in California, where the legislature last week approved, by a single vote, the first $8 billion for a Los Angeles-to-San Francisco high-speed rail line.

It could be on the Washington-to-Boston corridor, where Amtrak on Monday outlined a $151 billion proposal for 220-mile-an-hour trains by 2030.

Or it could be nowhere.

The new national transportation funding act signed by President Obama on Friday contained no money for high-speed rail, although the administration had sought about $8 billion a year. And Republican governors of Florida, Wisconsin and Ohio have spurned federal money for high-speed rail projects, sending the money back to Washington.

"There's no federal money, there's no private money, and states are not in a position to finance it," said Ken Orski, a transportation adviser to several Republican presidents, including George W. Bush. "The conference in Philadelphia will be high on rhetoric and talk of things going on in Europe and the Middle East . . . but in the domestic situation, their only hope is California."

Not so, says U.S. Transportation Secretary Ray LaHood.

"High-speed rail is alive and well in America," he said Monday. "The future is as bright as it's ever been.

"We will not be dissuaded by the naysayers in Congress. All over the country, ordinary Americans want to get off of clogged highways and have the kind of transportation they see in other countries. This is being driven by ordinary citizens."

Advocates of high-speed rail (defined as trains traveling at least 155 miles per hour) tout not only the transforming ability to travel quickly between congested cities, but also the thousands of jobs such projects create, their environmental benefits, and the economic gains they generate for high-speed corridors.

Critics point to the cost, especially at a time of record national deficits. Federal funds will be required to build any high-speed line, even if the trains ultimately pay for their own operation and maintenance.

The 500-mile California line would cost at least $68 billion to build, according to current estimates. The trip has been estimated at 2 hours and 40 minutes.

Amtrak estimates it would cost $151 billion to upgrade the Northeast Corridor and install a separate 438-mile high-speed line between Washington and Boston.

Not building high-speed rail could also have costs, according to the American Public Transportation Association, one of the sponsors of the Philadelphia conference.

A study issued Tuesday by APTA said "high-performance rail" networks in the Northeast, California, the Midwest and the Northwest could produce at least $660 million a year in time savings, unspent highway funds, and other benefits.

Many of the visiting foreign rail executives traveled to Washington on Tuesday to meet with administration and congressional high-speed rail advocates, and Rep. David Price (D., N.C.) told them, "I hope somehow your enthusiasm will be contagious in our own country."

Price blamed Republican leaders in the GOP-controlled House for blocking high-speed rail funds from the last three federal budgets, and he said Congress needed to balance budget-cutting with spending on innovative programs such as bullet trains. "We need a balanced approach that we're having a great deal of trouble getting consensus around," Price said.

He said high-speed rail in the United States "is not some kind of utopian fantasy, but it's clear that we have some work to do."

The leaders of high-speed rail companies from France, Italy, Spain, Russia, and Japan outlined the gains their countries had seen in jobs, congestion relief, economic development, and emissions reductions, but they acknowledged that high start-up costs required significant government investment.

In Spain, which has built 1,400 miles of high-speed rail lines since 1986, the cost has been about $32 million a mile, a representative said, and about $128 million a mile for tunnels.

Most Americans say they would likely use high-speed rail if it existed in this country, according to a survey released Wednesday by APTA.

But price would be crucial: 83 percent of respondents said it would be "very important" or "somewhat important" for the train to be cheaper than flying and 78 percent said it was important for the train to be cheaper than driving.

In other countries, the cost of traveling by high-speed train is often cheaper than flying but rarely cheaper than driving.

Support for high-speed rail is highest among young adults, the APTA survey found: 74 percent of those 18 to 24 years old said they would be "very likely" or "somewhat likely" to use bullet trains, compared to 62 percent among the entire adult population, and 45 percent among those over 65.

"Young people are focused less on driving and more on mobility, whatever the mode is," said APTA president Michael Melaniphy. "They see it as economically beneficial and environmentally as the right thing to do."

The obstacles the U.S. faces in its effort to develop high-speed rail include a lack of reliable funding, an overarching plan, and legislation to guide it, said a report released last month by the Mineta Transportation Institute at San Jose State University.

"Without a stable and reliable source of funding, the [high-speed rail] initiative will not succeed in the U.S.," the report concluded. "It is not far-fetched to imagine a scenario where a new administration could abandon the decision to build HSR altogether."

To avoid that, "the long-term funding plan has to be put in place," said Rina Cutler, Philadelphia's deputy mayor for transportation and an advocate of a high-speed rail line that includes stations at Market East and Philadelphia International Airport.

"We really want to be a cheerleader for high-speed rail," Cutler said. "It's crucially important for the country as a whole, and I think Philly is in a pretty significant location on the prime corridor in the country."

High-speed rail travel on the Northeast Corridor, with trips from Philadelphia to New York in 37 minutes, would spawn economic development and create thousands of jobs, she said.

"It will change the world as we know it," Cutler said.

Contact Paul Nussbaum at 215-854-4587 or pnussbaum@phillynews.com.