Ex-state Sen. Henry J. (Buddy) Cianfrani, whose political influence until three months ago ranked with that of Philadelphia's volatile mayor, Frank L. Rizzo, will plead guilty or no contest to 110 counts of racketeering, mail fraud, obstruction of justice and income tax evasion, his lawyer said today.

Such a plea, scheduled to be formally entered at a hearing Friday, would mark the end of the sharp slide from power that began in September with federal indictments on the charges.

Until he resigned from the post shortly after the allegations were made public, he was chairman of the state Senate Appropriations Committee in Harrisburg. He had parlayed that powerful position into an alliance with Rizzo that yielded him considerable back-room influence in Philadelphia's ward political system.

The Political demise of Cianfrani, who resigned as asenator two weeks ago, coupled with the conviction last April on obstruction of justice charges of another powerful Democrat, Herbert Fineman, former speaker of the state House of Representatives, has left Philadelphia without the clout in the state legislature to which it had become accustomed over decades.

The hoarse, balding Cianfrani, 54, was unavailable to reporters today, but his lawyer, Nicholas J. Nastasi, dictated a letter hand-delivered to U.S. District Court Judge Edward R. Becker, spelling out his client's intentions.

"Sen. Cianfrani has decided to waive his right to a trial and to plead guilty to all charged against him with the exception of the (4) tax counts to which a plea of 'nolo contendere' will be offered," the letter said.

"This decision comes after considerably profound deliberation by my client. The senator feels that since it has been determined by pretrial rulings that the charges are properly drafted, he should now publicly admit the degree of his culpability . . . His decision not to contest the charges is both unconditional and immediate."

South Philadephia politicians viewed this as an attempt on Cianfrani's part to throw himself on the mercy of the court and hope for lenient sentencing. "How much more can you do to a guy? He's given up everything - his senate seat is gone, he's broke and his career is down the drain," said one former ward leader.

The decision to plead guilty came after Nastasi failed in a pretrial motion to have incriminating tape recordings between the senator and grand jury witnesses ruled inadmissible as efidence at the trial, which had been scheduled for Jan. 4.

It also followed a series a of private discussions Nastasi had with federal prosecutors in the office of U.S. Attorney David W. Marston. Marston reportedly considered his case an exceptionally strong one and was unwilling to "plea bargain" for guilty peas to some of the counts in the indictment.

Specifically, Cianfrani was charged over a fouryear period with:

Receiving at least $52,000 in bribes from four parents to sponsor the admissin of their children into three medical and veterinary medicine schools.

Evading a total of $62,828 in federal taxes.

Spending $30,137 in state senate payrooll funds to hire a former girlfriend, Vera Domenico, of Cherry Hill, N.J., and her sisterinlaw, Evangelina Domenico of Philadelphia, in nonexistent jobs on the Appropriations Committee.

Trying to prevent Vera Domenico and her soninlaw, Ralph Valerinano, from testifying before the grand jury.

Close political associates of Cianfrani familiar with his thinking reported yesterday that another consideration in his decision to plead guilty was to spare another girlfriend, Laura Foreman, the ordeal of testifying at (Cianfrani has been separated from his wife for 20 years.)

Foreman accepted at least $10,000 in gifts from Cianfrani while she was covering local and national politics in 1975 and 1976 for the Philadelphia Inquirer.

In June, she was interviewed by FBI agents about Cianfrani and became a potential witness against him. After the Inquirer reported her relationship with the senator in August, she resigned from a reporting assignment she had only recently accepted with The New York Times.

Cianfrani grew up in the narrow streets of South Philadelphia packed with small rowhouses and just block away from the Italian market. His grandfather was one of the first Italian immigrants to settle in Philadelphia, and his father, Henry B. Cianfrani, a state legislator and ward leader in the 1950s and '60s, helped pave the way for his son's political successes.

Cianfrani took over the leadership of the second Ward from his father in 1955, was elected to his father's seat in the state house in 1962, and then rose to the stae senate in 1966.

By the mid1970s he had become one of the most powerful, in Harrisburg, by virtue of his chairmanship of the key Appropriation Committee.