Both released new commercials and battled over a slew of ­issues — including abortion rights, equal pay for women, and taxes — which they believe will swing the few undecided voters in what is considered one of the more important and competitive Senate races in the country.

Warren is planning a major rally Saturday with Governor ­Deval Patrick and Representative Michael Capuano, a Somerville Democrat, at Boston University’s Morse Auditorium, in an attempt to demonstrate the enthusiasm of grass-roots supporters.

Brown was in Washington for much of the week and has no ­announced events for Saturday. But on Friday, he continued traveling the state trying to demonstrate bipartisan support, getting an endorsement by Rita Mercier, a Democratic city councilor and former mayor of Lowell.

The intensity of the race will pick up even more over the next week. On Thursday, the two will meet face-to-face for the first time when they debate on WBZ-TV. Their series of four televised ­debates could have a strong ­impact on the race’s outcome.

Warren, who has been reshaping her ad campaign, was the first to air a negative ad on Thursday. Her 30-second spot, through the voice and image of a plain-spoken Lowell boxing trainer, accuses Brown of ‘‘siding with the big-money guys’’ and advocating tax cuts for the wealthy.

Brown immediately ­responded with an ad released Friday that shows the senator dressed casually in a sweater, looking directly at the camera.

“Instead of talking about things that matter, like jobs, she’s being dishonest about who I am and what I stand for,” Brown says in the new spot. “Don’t be fooled by Elizabeth Warren’s negative attacks. Like a lot of you, I came from nothing. I’m on your side, fighting for the middle class.”

In between shots of Brown, the ad shows fuzzy images of Warren and warmer shots of Brown greeting voters.

Brown has been attacking Warren on a campaign website but had not previously mentioned her in an advertisement.

Brown’s spokesman, Colin Reed, said Warren’s charges about Brown’s support of tax cuts for the wealthy are distorted.

“Scott Brown wants to keep taxes low on everyone,’’ Reed said in an e-mail. “He wants to keep existing tax rates (that have been in effect for more than a decade) in place.’’

Warren’s campaign responded that Brown voted against President Obama’s plan to ­extend the Bush era tax cuts for most taxpayers because it ­excluded those earning $250,000 or more a year.

Brown repeated Friday in an interview with WTKK that he would not support an extension of the Bush tax cuts, even if there was no other option on the table, unless it included all taxpayers, because he said many in the top bracket create jobs.

Brown created an additional flare-up Friday when he released a second advertisement that promotes his stance on abortion and other women’s ­issues. Brown has long said he supports abortion rights, ­although he has received the endorsement of Massachusetts Citizens for Life, the state’s leading antiabortion group.

The second ad comes as the Massachusetts Republican State Committee decided Thursday night to put off a decision on whether to adopt the national party’s platform until after the November election. Massachusetts Republicans have traditionally been more socially liberal than the national party. The state GOP’s current platform does not make a reference to abortion.

Brown’s ad features a variety of women praising him.

“Scott Brown is prochoice, and he supports a woman’s right to choose,” one woman says.

“I like that Scott Brown is ­independent; he really thinks for himself,” says another.

As the women speak, Brown is shown wearing his famous barn jacket, standing in front of his home with his two daughters, his wife, and their dog.

“When my daughters grow up, I want to make sure that they have good jobs with equal pay, and I know Scott Brown will fight for that,” one woman says.

Brown voted with other ­Republicans in June to block the Paycheck Fairness Act, saying it would spark lawsuits and unreasonably hamper employers. The bill would have ­required employers to provide a reason for disparities in pay, among other new requirements.