Four Republicans running for governor of Maryland pledged Thursday not to raise taxes if elected and heavily criticized the current administration’s handling of the rollout of its online health insurance exchange.

During a televised forum, all four of the candidates also proposed either repealing or making changes to the Common Core educational curriculum, and three of the four said they are steadfastly opposed to legalizing marijuana.

The debate, hosted by WBFF TV, the Fox affiliate in Baltimore, featured Harford County Executive David R. Craig, Del. Ronald A. George (Anne Arundel), Charles County businessman Charles Lollar and retired Baltimore firefighter Brian Vaeth.

None has managed to raise much money, and all four face uphill odds in a state that has elected only one Republican governor in the past generation. But they did their best to distinguish themselves Thursday night within a format that allowed one-minute responses.

While everyone ruled out raising taxes, Lollar said he would go further, promising to “eradicate some.” Lollar said his administration would look at eliminating the state income tax.

George, now serving his eighth year as a state delegate, told the audience that he has never voted for a tax increase and wants to lower personal income taxes by 10 percent.

Craig said that “no new taxes will be raised” if he’s governor and promised to cut the state budget by 5 percent during his first year. He said that he has a history of delivering balanced budgets and tax cuts as a county executive and mayor of Havre de Grace.

Vaeth, whose candidacy has received little media attention, said he, too, does not favor raising taxes.

All the candidates were critical of Maryland’s implementation of its online health insurance exchange. Enrollment has been hindered by technological glitches.

George said Lt. Gov. Anthony Brown, a Democratic candidate for governor, had not leveled with the public about problems with the exchange. Brown was charged by Gov. Martin O’Malley (D) with overseeing health-care reforms in the state.

“What he really did was keep us in the dark,” George said of Brown. George also called upon O’Malley’s health secretary to resign.

Craig said the state’s exchange is “a disaster.”

“They knew it was broken before they put it out,” he said.

Craig, a former schoolteacher, was also critical of the state’s embrace of Common Core, a set of national academic standards written by a group of governors and state education officials.

“Politicians should not be dictating what goes on in a classroom,” Craig said. “We should back off Common Core 100 percent.”

Lollar called for a “moratorium” on Common Care, while Vaeth said it deserves “another look.”

George said he is pushing a bill this session that would give local school boards in Maryland a say on the whether to adopt the standards.

All but one of the candidates said they are firmly opposed to following Colorado’s lead and legalizing marijuana. Bills are being pushed during the current 90-day legislative session to do just that, creating a system of regulation and taxation.

“Absolutely not,” said Craig.

“Absolutely not,” said George.

“No,” said Lollar.

Vaeth said he thinks legalization could help the economy.

Larry Hogan, a fifth GOP hopeful who plans to announce his candidacy next week, did not attend despite what debate moderator Mark Hyman said were “repeated invitations.” Hogan told The Post he did not participate because he is not yet a candidate.