Exhibit 8

 
                            _______________, 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. The discussion under that heading, to
the extent it describes the legal opinion of Arnold & Porter, reflects our
opinion, subject to the facts, representations, assumptions and other conditions
described or referenced therein.

    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.

    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,



                                        ARNOLD & PORTER