President Obama promised Thursday that his administration would "shortly" address the bipartisan chorus of questions about Rep. Joe Sestak's assertion that the White House offered him a federal job to stay out of the Pennsylvania Democratic Senate primary.

"I can assure the public that nothing improper took place," Obama said in response to a question during an East Room news conference, shedding no new factual light on the political mystery.

Sestak, by staying in the race, defied the White House and the rest of the party establishment, and last week he handily beat their choice for the nomination, five-term Sen. Arlen Specter, the Republican-turned-Democrat who delivered crucial votes for Obama's agenda.

Pressure has been mounting on the White House and Sestak to disclose what happened, with the Republicans on the Senate Judiciary Committee calling for a special prosecutor. The Justice Department already spurned a similar request from a top House Republican, Rep. Darrell Issa of California.

Democrats, too, have stepped up their calls for more disclosure, with some fretting that the job-offer controversy has swallowed up Sestak's campaign at a time he should be riding high from his primary win and laying out the case against GOP opponent Pat Toomey.

The White House and Sestak should come clean, or the issue will be "an ongoing distraction for Democrats," Gov. Rendell said Thursday. He said a special prosecutor was not necessary.

Obama said it would not be "weeks or months" before the administration's official response is released. Sestak said that someone from the White House called his campaign director, his brother Richard, on Wednesday to discuss the matter, the Associated Press reported.

In a television interview in February, Sestak said the White House offered him a job last summer, before he formally announced his Senate campaign. He has since declined to reveal details, as has the administration.

Presidents throughout history have used appointments as political tools to reward allies or to clear the path for a favored candidate, analysts say. Opinion is divided over whether it can be a crime.

A federal statute makes it a misdemeanor to offer a job or anything of value in exchange for a political act or to support or oppose a candidate, said Scott A. Coffina, a partner at Montgomery, McCracken in Philadelphia who was associate counsel to President George W. Bush from May 2007 to January 2009.

"It depends on how it was presented to Sestak," said Coffina, whose portfolio includes ethics issues. "If it was a vague 'there are other opportunities out there,' it might not be a problem." There may be a violation, he said, if there was a "more direct tie between the [specific] job and him dropping out."

No one has ever been prosecuted for offering a political job to clear a primary field, said Melanie Sloan, a lawyer who is executive director of the watchdog group Citizens for Responsibility and Ethics in Washington.

"It's impossible to imagine the Justice Department bringing such a case," Sloan said. "This is the way politics is played - it may be unseemly, but those are political questions, and no court is going to take them up."

Criminalizing routine acts of political dealmaking would cripple the ability of the government to function, she said.

Utah Gov. Jon Huntsman, a Republican mentioned as a possible 2012 presidential candidate against Obama, accepted the president's appointment last year as ambassador to China. "Was he bribed?" Sloan asked.

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