Democrats on both sides of the Capitol are using their new oversight powers to draw a bead on President Bush’s top political adviser, Karl Rove.

The House Oversight and Government Reform Committee plans to depose former Rove assistant Susan Ralston on April 5 as part of an investigation into contacts between former lobbyist Jack Abramoff and the White House.

The announcement of the deposition came on the heels of a March 29 letter from panel Chairman Henry A. Waxman, D-Calif., asking Rove to answer a series of questions about a presentation that Rove’s deputy, J. Scott Jennings, made to top General Services Administration officials about the 2006 election results and upcoming elections.

Waxman has also expressed an interest in obtaining e-mails that Rove and others may have sent and received using private e-mail accounts — rather than government accounts — to discuss government business.

Across the Capitol on March 29, Democratic senators on the Judiciary Committee grilled Kyle Sampson, the former chief of staff to Attorney General Alberto R. Gonzales, about Rove’s role in the Bush administration’s decision to fire eight U.S. attorneys.

The House Judiciary Committee has already approved subpoenas for Rove, Jennings, Sampson and former White House counsel Harriet Miers, setting the stage for a showdown with the White House over executive privilege.

Furthermore, the recent congressional testimony of former covert CIA agent Valerie Plame, whose outing led to the conviction on perjury charges of Vice President Dick Cheney’s former chief of staff, I. Lewis “Scooter” Libby, raises the possibility that Democrats will seek to question Rove about his role in that case.

Democrats have long obsessed over Rove, the political mastermind behind Bush’s electoral victories in 2000 and 2004. Even if they reveal no wrongdoing, they might be able to knock the White House political operation off track by giving operatives something to worry about.

In his letter, Waxman asked Rove to provide any documents or information relating to the use of federal agencies or resources to help Republican candidates.

Waxman also has written letters seeking documents from the Republican National Committee that could tie Rove to Abramoff, or tie Cheney to the defense contractors who bribed imprisoned former Rep. Randy “Duke” Cunningham, R-Calif. (1991-2005).

“I think it’s a big fishing expedition,” said Virginia Rep. Thomas M. Davis III, the top Republican on the panel.

Under Davis’s stewardship, the panel made its mark by hauling Major League Baseball stars into witness chairs to testify about steroids in their sport.

The hearings did not result in new federal law, but under the threat of statutory action baseball strengthened its strictures against steroids.

Davis’s predecessor, Republican Dan Burton of Indiana, used his gavel to turn the hearing-room entrance into a revolving door for Clinton administration officials.

Republicans stand ready to fight Waxman, and the political battles are just beginning. “I think we’re looking at a lot of issues of political interference,” said Waxman, who insisted he does not have any preconceived expectations of what he will find.

He released an e-mail in which Abramoff, the former lobbyist who pleaded guilty last year to bribing public officials and defrauding American Indian clients, asked Ralston to seek Rove’s intervention in an Interior Department matter involving Abramoff’s tribal clients.

Ralston had worked for Abramoff before being hired at the White House.

There did not appear to be a smoking gun in Ralston’s reply — “Will tell him” — but the effort to link Rove to the Abramoff scandal is tough to miss.

In another letter, sent to Joshua B. Bolten, the White House chief of staff, Waxman requests administration records involving contacts between administration officials and employees of MZM, the defense-contracting firm at the center of a scandal that resulted in an eight-year prison term for Cunningham.

Waxman notes that MZM’s first “prime” government contract was a $140,000, one-month billing for providing computers and office furniture to the Office of the Vice President. The letter requests that all records involving contacts between officials and MZM and its employees — not just those surrounding that initial contract — be delivered to the committee by April 6.