Maryland’s legislative leaders offered a lively preview Friday of what promises to be a 90-day session packed with contentious debates over tax increases to fund infrastructure projects, high-profile environmental issues, the expansion of gambling and same-sex marriage.

The two Democratic leaders of the legislature highlighted somewhat different priorities at a a gathering in Cambridge of the Maryland Association of Counties, while the Republican leader of the Senate urged the group to join him in looking out for the interests of the state’s rural areas.The new session starts Wednesday.

Appearing on the same panel, Gov. Martin O’Malley’s chief legislative officer, Joseph C. Bryce, forecast a busy stretch in which O’Malley (D) would press lawmakers to invest more in roads and other infrastructure, create incentives for the development of offshore wind power, curb the use of septic systems in new residential developments — and legalize same-sex marriage.

“On these issues of infrastructure investment, on these issues of the environment, you will see the governor providing leadership,” Bryce said. “You know, he wasn’t elected class president or homecoming king. He was elected governor. He has a responsibility to lead on these issues, and he will.”

O’Malley has floated the idea of raising the state’s gas tax to pay for transportation projects and its “flush tax” to pay for upgrades of water and sewer projects, but he has yet to offer specific plans for either.

Bryce noted Friday that the state’s gas tax of 23.5 cents per gallon has been unchanged since 1992, when gas was $1.08 a gallon, he said.

Senate President Thomas V. Mike Miller Jr. (D-Calvert) pledged that his chamber would pass the gas tax increase during the upcoming session even though it is unpopular, and he also touted his plans for expanding Maryland’s gambling program.

Miller said he would like to authorize table games at Maryland’s current five authorized slots sites — and allow a sixth casino in western Prince George’s County. Rosecroft Raceway and National Harbor are among sites that potential sites in that area.

Miller said the new site would draw customers from the District and Virginia.

“Politics is like war,” Miller said. “You hold onto your own, but you take from someone else.”

Miller also advocated increasing the current one-third share of proceeds that casino owners keep.

House Speaker Michael E. Busch (D-Anne Arundel) said recently that he sees a complicated path in his chamber for the addition of a new slots site because of the impact it would have on counties with previously authorized casinos.

On Friday, Busch vigorously defended the legislature’s decision last year on how to allocate additional funds for school construction that were generated by an increase in the sales tax on alcohol.

Senate Minority Leader E. J. Pipkin (R-Cecil), who repeated his accusation that Democrats are leading a “war on rural Maryland,” said that about 90 percent of that money went to urban school systems.

Busch said priority was given to counties from which lawmakers voted for the tax increase.

“Those who work get fed,” Busch said.

In rebutting Pipkin, Miller also said Friday that he would propose scrapping the estate tax for heirs of farmers whose land continues to be used for farming.