Exhibit 8

 
                            March 18, 1997



S&T Bancorp, Inc.
800 Philadelphia St.
P.O. Box 190
Indiana, PA 15701-3921


Ladies and Gentlemen:

    Reference is made to the information set forth under the heading "PROPOSED
MERGER-Certain Federal Income Tax Consequences" contained in the Proxy
Statement/Prospectus, which is included in the Registration Statement on Form S-
4 (the "Registration Statement"), filed by S&T Bancorp, Inc. ("S&T") with the
Securities and Exchange Commission (the "SEC") in connection with the proposed
merger (the "Merger") of Peoples Bank of Unity with and into the S&T Bank, a
wholly owned subsidiary of S&T. Subject to the representations, assumptions
and other conditions described or referenced therein, the description of 
anticipated material federal income tax consequences contained in the fourth 
through seventh paragraphs of that heading accurately sets forth our 
opinion.

    Our opinion is based on the case law, Internal Revenue Code, Treasury
Regulations and Internal Revenue Service rulings as they exist at the date
hereof. These authorities are all subject to change, and any such change may be
made with retroactive effect. We can give no assurance that, after such change,
our opinion would not be different. We undertake no responsibility to update or
supplement our opinion following the effective date of the Registration 
Statement.

    We hereby consent to the filing with the SEC of this opinion as an exhibit 
to the Registration Statement and to the reference to our firm under the heading
"PROPOSED MERGER-Certain Federal Income Tax Consequences" contained therein.
In giving such consent, we do not thereby admit that we are in the category of
persons whose consent is required under Section 7 of the Securities Act of
1933.


                                        Very truly yours,

                                        /s/ Arnold & Porter

                                        ARNOLD & PORTER