Members of Maryland Gov. Martin O’Malley’s administration sought Tuesday to allay fears of Republican senators that a transportation bill being debated in the closing weeks of the 90-day session would offer little to their largely rural constituents.

At a hearing of the Budget and Taxation Committee, Sen. George C. Edwards (R-Garrett) acknowledged that the legislation introduced by O’Malley (D) — and approved last week by the House of Delegates — is likely to pass before lawmakers adjourn April 8.

But Edwards and others Republicans said the plan relies too heavily on gas tax increases and that too much of the money would go to high-profile mass transit projects such as the Purple Line in suburban Washington and the Red Line in Baltimore.

“You’re putting all the burden on the vehicle operator,” Edwards said.

That view was echoed by Sen. David R. Brinkley (R-Frederick), who accused the administration of taking “the lazy way out.” Brinkley said the bill should draw more tax revenue from the urban regions that will benefit from proposed rail projects. As written, the bill only calls for a study of that concept.

Both Matthew D. Gallagher, O’Malley’s chief of staff, and Acting Transportation Secretary Darrell B. Mobley, sought to assure the senators that some of the new money generated by the legislation would be used for road safety projects, bridge repairs and commuter bus service in rural parts of the state.

“Maryland has unique needs for each region,” Mobley said.

Sen. Richard F. Colburn (R-Dorchester) was among those who were not persuaded.

“To me, there’s no reason for anybody from the Eastern Shore to support this,” he told his colleagues.

Senate President Thomas V. Mike Miller Jr. (D-Calvert) has been a champion of increased transportation funding and has pledged to work to round up the votes to pass a bill in his heavily Democratic chamber.

Under the version of the bill passed by the House last week, motorists could expect to pay roughly an additional 13 to 20 cents a gallon by mid-2016, according to legislative analysts. The higher gas taxes would be phased in over several years, with the first increase of about 4 cents a gallon coming in July.

Transportation officials say the bill would yield $4.4 billion for roads and mass-transit projects over the next six years, including additional borrowing.

The plan adds another layer of taxes to purchases of gasoline, which are now subject to a 23.5-cent-a-gallon flat tax, a levy unchanged since 1992.

Under the bill, a new sales tax of 3 percent also would be imposed. That tax would be phased in over three years, starting in July.

Another 2 percent could later be tacked onto the sales tax on gas if Congress doesn’t take action on a separate issue related to Internet sales.

Maryland and other states are lobbying the federal government to adopt a long-stalled plan that would ensure states can collect sales taxes when their residents make purchases from out-of-state Internet retailers.

If Congress acts on that by 2015, that revenue would be earmarked for transportation in Maryland. Otherwise, the additional 2 percent sales tax on gas would take effect.

Virginia has a similar provision in the transportation bill passed last month that was championed by Gov. Robert F. McDonnell (R).