Senate hopefuls launching their first wave of ads today

Venture capitalist Stephen Pagliuca, who officially launched his candidacy yesterday, has purchased $500,000 worth of television air time across the state. In his first 30-second ad, he describes his professional background and promises to travel across the state to talk to voters. He said he is running to bring a “new way of doing business in Washington.’’

His campaign plans to run the ad for a week, but Pagliuca, who is estimated to be worth $400 million, is expected to continue advertising heavily until the Dec. 8 primary.

US Representative Michael E. Capuano, a six-term Somerville Democrat, will declare his candidacy today at Boston’s Omni Parker House, having bought $300,000 to $400,000 worth of statewide television ads that will run for the next several weeks.

His 30-second ad is an effort to appeal to the party’s liberal wing, which dominates primary elections. It says that Capuano stood with Kennedy in opposing the Iraq war, that he opposes the death penalty, and that he is a strong advocate for a strong public health insurance option.

Mike Shea, a veteran Democratic media consultant working for Capuano, said the spot is designed to “acquaint [voters] with the fact that he is the candidate who most closely mirrors Senator Kennedy’s record on the important issues.’’

Yesterday, Pagliuca tried to tie himself to Kennedy, praising him in his remarks as the greatest senator in state history. But he also had to field a number of questions as to why he wanted to end Kennedy’s Senate career in 1994 by supporting challenger Mitt Romney in the general election.

Pagliuca said he had donated to and backed Romney’s candidacy out of personal loyalty, because Romney had hired him at Bain Capital in 1989 and was a personal friend. It was, he said, a “case of friendship coming before politics.’’ Pagliuca said he has always been a progressive Democrat, but he was a registered Republican in the 1990s and has donated to Republicans, including $5,000 to the state GOP.

“You have to be loyal to your friends,’’ Pagliuca, a co-owner of the Boston Celtics, told reporters at a press conference at the TD Garden’s Legends Club. He said he has donated $131,000 to Democratic candidates and committees, “10 times’’ more than what he has given to Republicans.

With his wife, Judy, and two teenage sons standing behind him, Pagliuca referred to having worked with Kennedy on health care. He said Kennedy had encouraged him to run for public office as the “venture capital guy’’ on “the right side’’ of the issues. He also defended his role as a private equity investor, arguing that he has created far more jobs than have been lost when his investments failed.

His experience building businesses and creating jobs, he said, will bring another perspective for Democrats in Washington. “I bring something different to the party,’’ he said.

Still, there is some skepticism about his candidacy and his assertions that he is a progressive.

“I have been told that he’s a bit of a progressive Democrat, and I also understand that he’s a Bain guy,’’ said Robert J. Haynes, president of the Massachusetts AFL-CIO. “It would surprise me if there are progressive Democrats over there, but, hey, we’ve got to give the guy a chance to give us his political views.’’

Meanwhile, the third major candidate in the Democratic race, Attorney General Martha Coakley, continued to roll up union endorsements, including from another Teamsters local, showing she has strong support in an active base within the Democratic Party.

Declared Republican candidates include state Senator Scott Brown of Wrentham and Robert Burr, a Canton selectman.

Former Red Sox pitcher Curt Schilling, an independent who has often supported Republicans, told WEEI-AM yesterday that he remained “on the fence’’ about running.

Michael Levenson of the Globe staff contributed to this report.