Maryland gubernatorial hopeful Doug Gansler unveiled a new television ad Thursday that knocks Democratic rival Anthony G. Brown for skipping a televised debate this week. (YouTube: Doug Gansler)

The Maryland gubernatorial campaigns of Douglas F. Gansler and Anthony G. Brown both unveiled negative ads targeting the other Thursday, marking a new phase of the television campaign in the bitter Democratic primary.

Gansler, the state’s attorney general, hit Brown, its lieutenant governor, for skipping a televised debate this week.

“If Anthony Brown won’t even show up in Baltimore to debate, how can we trust him to stand up for us as governor?” the ad asks, as viewers see footage of Tuesday night’s debate on WBFF-TV between Gansler and Del. Heather R. Mizeur (D-Montgomery).

An empty podium set up on the stage for Brown is visible in the 30-second ad, which Gansler aides said would start airing Thursday in the Baltimore market.

Hours later, the Brown campaign announced that it was responding with a 30-second ad questioning Gansler’s support for cutting the corporate income tax rate while proposing a more limited expansion of pre-kindergarten programs than his two Democratic rivals.

“I think he sounds like he is for corporate interests,” a voter in the ad says in response.

“I would think he was a Republican,” another says.

Brown aides said the ad attacking Gansler — which includes footage of Gansler talking about his plans — would start airing in Baltimore on Friday and would also appear in the Washington television market. Brown has pressed a similar argument against Gansler in direct mail pieces in recent weeks.

While both Brown and Gansler have been airing commercials for months, the two spots previewed Thursday are the first to mention the other candidate by name.

Brown, the front-runner in the June 24 primary, has said he decided not to participate in the WBFF debate because it violated an agreement among the three campaigns to have only three debates. His opponents offered a different interpretation of the accord, saying that they agreed to three televised debates — and that a radio encounter in which they and Brown plan to participate next week does not count.

At an event in Baltimore on Wednesday, at which Brown picked up the endorsement of the League of Conservation Voters, he was peppered with questions from reporters about his decision to skip Tuesday’s debate. He said repeatedly that he is looking forward to another televised debate scheduled for Monday night.

“The lieutenant governor is very excited about the two debates next week in Baltimore,” Brown campaign manager Justin Schall said Thursday, referring to both the televised debate to be hosted by WBAL-TV and Maryland Public Television and one set for Thursday on Baltimore radio station WOLB-AM.

Brown also took part in the first televised debate among the three Democrats, which was held at the University of Maryland on May 7.

Gansler’s has proposed gradually reducing Maryland’s corporate income tax rate from 8.25 percent to 6 percent, which would match the rate in Virginia.

Under Gansler’s proposal, the corporate tax rate would drop by a quarter percentage point annually — meaning it would take at least nine years before it hit 6 percent. Aides say Gansler would slow the pace of the phase-in if the cuts weren’t having the desired effect on the economy.

Both Brown and Mizeur have questioned whether the state can afford the lost revenue.

Gansler contends that the lost revenue would be offset by growth in the tax base as Maryland becomes a more attractive location for corporations. He has also proposed closing a corporate tax loophole that he says would offset part of the lost revenue.

All three major Democratic candidates for governor have offered plans to expand taxpayer-subsidized pre-kindergarten education. Of the three plans, Gansler’s is the least ambitious and the least costly.

Gansler has pledged to expand the state’s current pre-K offerings from half-day to full-day programs and increase the eligibility cutoff from 185 percent of the poverty level to 300 percent.

He has said that expansion beyond that is not affordable in the short term but that he would like to make pre-K “universal” at some point in the future, as his rivals have proposed more immediately.