A few days after he switched parties, Sen. Arlen Specter went on

Meet the Press

and hotly denied reports he had promised President Obama he would be a "loyal Democrat."

In dozens of conference calls and meetings since then, Specter has been trying to reassure Democratic elected officials, county chairs, and party activists around Pennsylvania of the opposite proposition: that he can be counted upon to support the president.

Participants in these efforts say that Specter has been relaxed and direct as he lays out his case, dwelling on instances in which he bucked his former Republican Party during a 29-year Senate career. Specter has been received well, they say, though some skeptics are eager for a Democrat with a more liberal record to challenge him in the 2010 primary.

"I've read about his diligence before, but I've been really impressed to see how they're reaching down to the very base of the grass roots," said Jack Hanna of Indiana County, chairman of the state party's Southwest caucus, who was on two conference calls with Specter. "The guy's on top of it."

This weekend, Specter faces the biggest public test so far of his appeal to party regulars, appearing at the Democratic State Committee spring meeting in Pittsburgh. He is scheduled to host a dessert reception after a fund-raising dinner tonight and to make a major speech tomorrow.

U.S. Rep. Joe Sestak of Delaware County, who has said he intends to run against Specter for the Democratic nomination, also plans to attend.

On Monday, Specter had a breakfast meeting with Democratic leaders in Montgomery County, moved on to Delaware County for lunch, and met with Chester County leaders in the evening.

At the Montgomery gathering, held at the Hilton Garden Inn in Fort Washington, Specter faced a couple of challenging questions about his support for key elements of former President George W. Bush's agenda, including the tax cuts for the wealthy and the Iraq war.

"He was one of the enablers in the Senate because, as a moderate with a lot of seniority, he was in a position to stand up to Bush," said Montgomery County Commissioner Joe Hoeffel. "I have a hard time getting past that."

Hoeffel, the Democratic nominee against Specter in 2004, asked him about those issues. Their exchange was cordial, Hoeffel said.

"Everybody respects Sen. Specter's intellect, long service, hard work, honesty, and integrity," he said. Hoeffel mused that it could not be easy for his old foe to change parties and that the switch was "a little disorienting" to some Democrats.

Several local candidates in the audience also asked whether Specter would do a fund-raising or campaign event for them.

"There's a lot of residual goodwill," said Montgomery County party chairman Marcel Groen. "Most folks think he's now the incumbent Democratic senator, and we should coalesce around him."

In calls and meetings, Specter also has been questioned about his opposition to the Employee Free Choice Act, the top agenda item of organized labor, because of a provision that would allow workplaces to be unionized without a secret ballot. Specter stressed his role in trying to work out a compromise that would rescue the bill, participants said.

Chris Nicholas, Specter's campaign manager, said that Specter had participated in at least 10 conference calls and nearly as many meetings in the last several weeks - as he has for years.

"The senator has an ongoing political outreach effort," Nicholas said. "The only new part is who he's reaching out to."

Gov. Rendell and state party chairman T.J. Rooney have joined most of the conference calls, introducing Specter and talking about all he has done for the state.

"The thing that did strike me was how many people, particularly among the elected officials, knew him from the retail campaigning he has done over the years," Rooney said.

After more than four decades as a Republican, Specter switched parties April 28 and is running for a sixth term as a Democrat, with the full backing of the White House, Rendell, and other party leaders.

Sestak, a second-term congressman who had been considering a run for the Senate before the change, has all but announced he will challenge Specter. He argues that it is not right for the party establishment to try to anoint the Senate nominee.

If he pursues the race, Sestak will be betting on the idea that rank-and-file Democratic primary voters might feel less warmly toward the new guy than most of the party's leadership.

A Susquehanna Polling & Research survey released earlier this week suggested an opening. It found that 63 percent of likely Democratic primary voters surveyed said that Specter should be challenged in the primary.

Contact staff writer Thomas Fitzgerald at 215-854-2718 or tfitzgerald@phillynews.com.