BOSTON (AP) — Republican state Rep. Daniel Winslow said Tuesday that he was forming an exploratory committee and was likely to be a candidate in a special election for the U.S. Senate seat formerly held by Secretary of State John Kerry.

Winslow, a former judge who was chief legal counsel for two years in the administration of former Gov. Mitt Romney, told reporters he was speaking with party activists, potential donors and others about the race. He gave no timetable for a definitive announcement.

‘‘I'm about 99 percent there, but I need to make sure the Republicans in Massachusetts want me to take that step,’’ he said.

The primary is scheduled for April 30, followed by the special election on June 25.

The Massachusetts GOP has been struggling to find a candidate since former U.S. Sen. Scott Brown announced on Friday that he would not run for Kerry’s seat. Since then, several other high-profile Republicans, including former Gov. William Weld, former Lt. Gov. Kerry Healey and Romney’s son, Tagg, have all said they would not be candidates.

Two Democratic congressmen — Edward Markey and Stephen Lynch — are running for the Democratic nomination to replace Kerry, who left the Senate last week to become Secretary of State.

Gov. Deval Patrick named his former chief-of-staff, Mo Cowan, to fill the seat on an interim basis until the special election is held.

A native of western Massachusetts who now lives in Norfolk, Winslow, 54, was elected to the state House of Representatives in 2010 and reelected to a second term last year.

Winslow has positioned himself as a fiscally conservative but socially moderate Republican who is pro-abortion rights and has been endorsed by the Gay and Lesbian Political Caucus.

‘‘I just don’t know if there is sufficient support in the Republican establishment for that kind of Republican,’’ he said.

While citing a ‘‘B'’ rating from the National Rifle Association, Winslow said he supported a discussion of ways to reduce gun violence, but would not immediately say if he supported reinstatement of a federal ban on assault weapons. He promised to issue detailed position papers on various issues once he makes a final decision on running.

Winslow served as Romney’s chief legal counsel from 2003-2005. He was asked if his past ties to Romney could be a potential negative in Massachusetts, where voters soundly rejected the former governor in favor of President Barack Obama in the last presidential election.

After joking that he wished he had Romney’s money, Winslow said he was proud of his service in the Romney administration and of his friendship with the former governor.

‘‘But I'm Dan Winslow, I'm not Mitt Romney,’’ he added.

Democratic officials were quick to find fault with Winslow.

John Walsh, chair of the Massachusetts Democratic party, said Winslow was in Romney’s ‘‘inner circle’’ and served as one of Romney’s ‘‘apologists and political attack dogs’’ during the presidential campaign.

Winslow also showed more interest in ‘‘grabbing headlines’’ than getting work done in the Legislature, Walsh contended in a statement.

According to Federal Election Commission regulations, prospective candidates may form exploratory committees to test the waters, and conduct limited activities such as polling, travel and making phone calls to gauge support. An exploratory committee is not considered a political committee and does not have to file finance reports until actual campaigning begins.