WASHINGTON — The nation's public transportation systems logged a 5.2 percent jump in ridership in the second quarter, according to industry figures to be released today, as record-high gas prices pushed people to take millions more trips on buses and rail systems.

Riders made a total of 2.8 billion trips on the nation's subways, buses, commuter railroads and light-rail systems from April to June, according to the Washington-based American Public Transportation Association. That's up from 2.7 billion in the same period last year.

By contrast, transit ridership increased 2.1 percent for all of 2007, a more typical growth rate.

The surge in riders is straining many agencies that don't have the funds to expand service. Many systems are struggling just to maintain the service they already offer because of their own rising fuel costs, according to a survey conducted by the association.

"The irony is that just at a time when Americans need choice, need alternatives to higher-priced gasoline, 35 percent of transit systems are saying they may need to cut service," association president William W. Millar said. His group is pushing for more federal funding for public transportation.

In the meantime, transit agencies are looking at creative ways to meet the growing demand. In New York City, officials are planning to experiment with seatless subway cars next spring to squeeze in more riders. The cars would have only fold-down seats, all of which would be locked in the up position during rush hour. In Boston, the Massachusetts Bay Transportation Authority is using longer trains on the T and increasing the frequency of some bus and rail services.

The soaring demand has been felt in small agencies, too. In Madison, Wis., buses operated by Metro Transit are often too full to stop for waiting passengers. It may take up to 15 minutes for the next bus to arrive, said Colin Conn, the agency's schedule planner.

Metro Transit tries to fix the problem by running out an extra bus to pick up the overflow — something it typically has to do dozens of times a day when the University of Wisconsin is in session, Conn said.

The Chicago Transit Authority has reported surging ridership for months, including a 10 percent year-over-year increase in August, but that hasn't helped its bottom line. On Monday, the agency announced it would cut 80 jobs and make other efforts to trim costs.

In Washington, where the rail system had its busiest month ever in July, Metro General Manager John Catoe is pushing for bus-only lanes as a way to encourage people to ride buses and relieve pressure on the crowded subway. The idea requires only "paint and a few signs," but taking away lanes from private vehicles could be politically tricky, Catoe said.

Transit advocates say what is ultimately needed is more federal support. A bill to make $1.7 billion available to transit agencies during the next two years passed the House in June. Millar and other transit advocates are scheduled to testify Tuesday today at a Senate committee hearing.

Opponents of increased transit funding point out that even with the ridership gains, the vast majority of people still drive. Ron Utt, of the conservative Heritage Foundation, said transit is "inconsequential in terms of reducing congestion or greenhouse gases" and that people who want to use transit should simply pay more.

Citing the example of a Washington-area commuter rail, Utt said: "If more people want to use that and more people have to stand, I don't know why that should place a financial burden on people in Iowa."

Although gas prices have eased since July, transit officials predicted that would do little to stem the growth in ridership.

"A lot of people who have been paying the high gas prices have used their credit cards to pay for it," said Catoe, of the Washington Metro. "Those bills are coming due."