A longtime political consultant and former member of state Sen. Vince Fumo's inner circle agreed yesterday to plead guilty to cheating on his taxes.

Howard J. Cain, 60, of Wayne, also agreed to testify for the prosecution at Fumo's trial in September that he conspired with Fumo and others to defraud the state Senate.

Fumo has been charged with defrauding the state Senate, a charity and a museum, in addition to trying to thwart an FBI investigation.

The veteran lawmaker, who decided not to seek re-election this year, has pleaded not guilty to the charges.

Authorities said that Cain failed to report more than $1.6 million in income to the IRS between 1997 and 2006, and owed unpaid taxes of more than $411,000.

Cain failed to file tax returns from as far back as 1991. The feds said that income that Cain received from 1991 through 1996 couldn't be quantified because of inadequate records.

Cain was a political consultant for more than 30 years and had been involved in more than 80 campaigns, but court papers filed yesterday suggested that Fumo was his patron.

The feds said that Cain's largest single source of income from 1991 to 2006 came from consulting services to the state Senate Democratic Appropriations Committee.

Fumo chaired the committee from 1985 until his indictment in February 2007.

The feds said that beginning in 1985, after Cain assisted the South Philadelphia Democrat in a successful re-election campaign, his company, Venture Analysis Inc., received a contract from the committee and continued to receive annual contracts through 2006.

From 2000 through 2006, Cain's firm received annual payments between $73,500 and $88,000 under the contracts, court documents said.

As part of the plea agreement, Cain stipulated that he conspired with Fumo and others to bilk the state Senate by submitting bogus invoices under a contract with the committee that resulted in payments to Cain for doing political campaign work in violation of state law.

Cain was not charged with misusing state funds, which resulted in losses of more than $200,000, but the uncharged fraud can be used to determine an appropriate guideline-range sentence, the plea agreement said.

Cain could potentially face 30 to 37 months behind bars under advisory sentencing guidelines.

Cain also agreed to pay restiution of $411,303 to the IRS for tax years 1997 through 2006, plus interest.

Cain's deal with the feds could bolster their case against Fumo.

Rather than rely on the testimony of other witnesses or records, the feds can now put somebody on the witness stand who was involved in every Fumo campaign since the mid-1980s, was part of Fumo's inner circle and who has admitted that he conspired with Fumo to defraud the state Senate.

Prosecutor John Pease said that because of the pending Fumo trial, it would be inappropriate to comment.

Peter Scuderi, Cain's attorney, declined comment. A plea hearing will likely be held in the next couple of weeks.

Fumo's lawyer, Dennis J. Cogan, and Fumo spokesman Gary Tuma also declined comment. *