Former Gov. Don Siegelman went on trial Monday on charges he swapped political favors for gifts and campaign donations in deals with former HealthSouth CEO Richard Scrushy and two of his cabinet members.

Siegelman "took the executive branch of state government and he turned it into an unlawful enterprise," chief prosecutor Louis Franklin told jurors in his opening statement.

Siegelman, a Democrat who was governor from 1999 to 2003, is charged with bribery and extortion. He insists the charges are an effort by Republican prosecutors to derail his campaign for a new term as governor and his lawyers told jurors Monday the charges are based on lies.

Siegelman has promised to stay in the race for the Democratic nomination even though the trial coincides with the final weeks of the campaign before the June 6 primary.

Franklin spent about an hour outlining his case, saying the government will prove that Siegelman traded state contracts, appointments and favors from his office for cash, gifts and campaign contributions.

He said Scrushy had backed Siegelman's opponent in the 1998 gubernatorial race that Siegelman won, and the HealthSouth executive had to scramble to find a way for the new governor to let him stay on a state board overseeing hospital development.

"He had to bribe our governor," Franklin said.

He was followed by Siegelman's attorney, Vince Kilborn, who said the government's case was built on lies by witnesses who have pleaded guilty in the case and are trying "to save their own skin by coming in and telling you things that are not true."

The government's chief witnesses, former top Siegelman aide Nick Bailey and lobbyist and landfill developer Lanny Young, have pleaded guilty in the probe and await sentencing.

"The government is going to have to call a bunch of liars, a bunch of con artists, a bunch of thieves," Kilborn said.

Siegelman also is charged with racketeering and obstruction of justice, along with former Chief of Staff Paul Hamrick. Former state Transportation Director Mack Roberts is charged with mail and wire fraud involving road deals.

Scrushy is charged with bribery and mail fraud involving $500,000 in campaign donations to Siegelman to support establishing a state lottery, which the government describes as a payment to keep Scrushy's seat on the hospital regulatory board.

The judge has told jurors the trial could last four to six weeks.

On Monday, the judge allowed Scrushy to add a prominent black lawyer to his defense team. Attorney Fred Gray represented Rosa Parks when she challenged Montgomery's segregated buses by refusing to give up her seat to a white man in 1955.

Scrushy, who is white, had support from black ministers when a jury of seven blacks and five whites acquitted him of criminal charges last year in Birmingham.

In May 2004, a separate federal grand jury in northern Alabama indicted Siegelman on charges of conspiring to rig bids on state Medicaid contracts while serving as governor. That case ended when a federal judge ruled there was insufficient evidence to support the main charge.

Scrushy was acquitted by a federal court jury in Birmingham in June 2005 on all charges in the criminal case stemming from the massive accounting fraud at HealthSouth, the Birmingham-based medical services chain he founded.