America is bracing itself for a series of investigations that could see top officials from the administration of President George W Bush hauled in front of Congress, grilled by a special prosecutor and possibly facing criminal charges.

Several investigations will now cast a spotlight on Bush-era torture policy and a secret CIA assassination programme, examining the role played by big names such as the former vice-president Dick Cheney and the former defence secretary Donald Rumsfeld.

In one investigation into the controversial firing of federal prosecutors, Bush's political guru, Karl Rove, has already been forced to appear before Congress and give testimony behind closed doors. Another investigation, by the House of Representatives' intelligence committee, has already asked for documents from the CIA and has now announced that it will examine the legality of keeping a secret CIA hit squad hidden from Congress, something alleged to have been ordered by Cheney himself.

"I intend to make this investigation fair and thorough," said the committee's chairman, Texas congressman Silvestre Reyes late on Friday.

The moves reveal a long-awaited desire by elements of the Obama administration and Democrat-controlled Congress to examine alleged abuses of power by Bush officials. They also raise the prospect of a bitter political fight with Republicans, who are likely to portray any attempt to investigate leading Bushites as a witch-hunt.

The inquiries also seem to go against the wishes of some in the White House, including Barack Obama. The president has said he does not want to be distracted by the past and instead intends to focus on economic recovery and healthcare reform. "The White House is more in the mood for going forward on the issues, such as healthcare, by which they want to define their presidency," said Gary Schmitt, a former intelligence official under Ronald Reagan and a fellow of the American Enterprise Institute.

But Obama may not have too much say in what could be the most explosive investigation: one set to be launched by the attorney-general, Eric Holder. Holder is mulling whether to appoint a special prosecutor to examine CIA activities since 2001, focusing on the use of torture in interrogation of terror suspects. Any such prosecutor could have the power to bring criminal charges.

Obama has made clear that the final decision is Holder's alone and news reports last week indicated that Holder was "leaning" towards making such a move. The prosecutor's mandate could be narrowly focused on minor officials or broadened to reach the top levels of Bush's cabinet.

Holder's decision will be influenced by the results of numerous reports on his desk. One, a survey on interrogation techniques, carried out by the CIA's inspector-general, is due to be made public at the end of this month. Holder spent two days reading the report and friends have said he was "shocked and saddened" by its contents.

Another report, to be released in the next two months, is being compiled about top officials in the Justice Department who drew up legal advice that justified the new interrogation techniques. That probe focuses on John Yoo, a former deputy assistant attorney general and Jay Bybee, a federal judge.

Many insiders think public reaction to those two reports is likely to ensure that Holder eventually appoints a special prosecutor, similar to Kenneth Starr, who investigated Bill Clinton's affair with Monica Lewinsky. "I think it is likely that Holder will do that," said Larry Johnson, a former senior CIA official.

At the same time, other senior politicians in Congress are investigating the CIA's activities in the Bush era, especially allegations that it kept hidden a secret assassination squad aimed at top al-Qaida figures. The Senate could announce its own investigation alongside the House one already now going ahead. Both could subpoena officials, perhaps including Cheney.

One member of the House committee, New Jersey congressman Rush Holt, told his local newspaper that the inquiry should be as intense as the that of the committee which investigated Watergate. "I think any new investigation will produce revelations that are as jaw-dropping as those that were uncovered by the Church committee," Holt said.

These fresh investigations would add to some already under way. Rove is expected to be called again for further questioning later in the summer. Obama has ordered his national security officials to examine allegations that Bush officials resisted efforts to investigate a massacre of hundreds of Taliban prisoners in 2001 by an American-backed Afghan warlord. "I've asked my national security team ... to collect the facts for me that are known and we'll probably make a decision ... once we have all the facts," Obama said during his recent trip to Africa.

A series of hard-hitting investigations will be celebrated by many on the liberal wing of the Democratic party and human rights activists. "We have the right to be informed of our government's failed and egregious policies. Our recent history has taught us that the rule of law is meaningless if left unenforced," said Michael Macleod-Ball, a director at the American Civil Liberties Union.

However, there could also be a political price. Many former intelligence officials are furious that the CIA is being dragged into politics. "It is pure politics. It is just crazy," said Johnson.

Others say protracted investigations will sap Obama's political capital at a time when he faces a difficult battle over healthcare reform. Indeed, some conservatives might relish the prospect of rehashing old debates over anti-terror tactics. Cheney himself, who led a secretive life in office, has been a happily public voice defending Bush policy since he left office and he has strong support from the conservative media.

One parallel might be the Iran-Contra hearings of the 1980s, when a secret plan to ship arms to Iran to raise money for Nicaraguan rebels made Colonel Oliver North - who helped craft the scheme - a patriotic folk hero. "Republicans will be happy if Democrats want to go down this road. They are happy to have a debate about national security. You could easily see someone have another 'Oliver North moment'," said Schmitt.