Votes are lined up to appoint a senator

In a key development, House Speaker Robert A. DeLeo, who has been publicly noncommittal, made a decision to back the proposal and was privately calling members yesterday to make the case. House vote-counters said support among lawmakers numbers in the mid-80s - more than enough in the 160-member body.

Patrick has signaled privately that he’d like to sign the bill by Friday and make an appointment within days, possibly having an interim senator in place by next week.

But in the other chamber, Senate President Therese Murray has remained far more reserved in her support, talking with senators but not advocating for the change, according to Senate sources.

One high-ranking Senate official familiar with the vote count said the numbers are there for passage - but narrowly. It is that chamber that Republican Richard Tisei, the Senate minority leader, will try to table the bill with the hopes of delaying it beyond its usefulness, or shaming Democrats who are on the fence over to his side.

“The fact that they think this is going to move like a knife through a stick of butter - that this is going to be a ‘shazamm’ bill that goes through - well, it’s not,’’ Tisei said in an interview last night. “We’re going to slow it down.’’

Republicans don’t oppose the concept of an interim senator, but they think it’s unfair for Democrats to change the law for this appointment.

Murray and DeLeo both declined to comment last night.

Passage would reverberate from Beacon Hill to Washington on an issue that has been a focal point of Massachusetts politics since Edward M. Kennedy’s death last month.

Top Democrats in Washington have been aggressively pushing for Massachusetts to temporarily fill the seat to give them more leeway in approving President Obama’s national health care plan. Shortly before his death, Kennedy himself advocated for the change in law.

Under the rules of the state Senate, the minority party could hold up the measure for up to five sessions. Whether those delays take place over several weeks or several days depends on how Murray sets the schedule. She could call for a session every day next week, for example, and Tisei would be out of delay tactics by the end of the week.

Murray could also opt to hold consecutive sessions in a single day, a move she has never done. She is unlikely to take that approach, according to senators close to her.

She has been under significant pressure, though, to take a more active role, fielding phone calls in recent weeks from White House senior adviser David Axelrod, US Senate majority leader Harry Reid, and Kennedy’s widow, Vicki.

“I feel quite optimistic that we have the votes on the Senate side,’’ said state Senator Robert O’Leary, a Barnstable Democrat and top supporter of the proposal. “People have thought about the significance of it and people have started moving in a position in support of it.’’

He estimated that supporters in the Senate had a margin of roughly three votes.

Meanwhile, the joint Election Laws Committee began voting yesterday on the measure in anticipation of a vote by the full House tomorrow.

The legislation, which went out at 11 p.m. Monday to members of the committee, would require any appointee to come from the same political party as the person who previously held the office. The appointee would serve for about four months, until a special election on Jan. 19 fills the seat for the remaining two years of Kennedy’s term.

“If the voters wanted a Democrat to serve until 2012, it’s only fair for the interim to be of that party,’’ said state Representative Michael Moran, a Boston Democrat and a cochairman of the committee.

The 17-member committee was told to register their votes by 11 p.m. tonight. The committee cochairs both expect it to be approved, but not without opposition.

“I believe that the time has elapsed for our opportunity to do something,’’ said state Representative Paul Kujawski, a Democrat from Webster and a committee member who plans to vote against the change. “We changed the law, we’ve made a commitment. . . . I believe that’s what we have to stick by.’’

The legislation would not prohibit an interim appointee from seeking the seat permanently, a requirement that some fear would be unconstitutional. Instead, House and Senate lawmakers are considering a resolution that would make it clear that they don’t want the appointee to run for the seat.

Attorney General Martha Coakley, the only Democrat so far to formally announce a candidacy for the US Senate, said yesterday that she supported the change. She said she has expressed her views to Murray, one of her top supporters.

“We know how Senator Kennedy would have voted on many of the important issues coming before the Congress this fall,’’ Coakley said. “But . . . whether I win this race or someone else wins, it’s going to be a lot easier . . . to be able to pick up where an interim senator and staff have kept up the work for the people of Massachusetts.’’

Matt Viser can be reached at maviser@globe.com.