Exhibit 5.1


                                  June 10, 1998




Board of Directors
Hagler Bailly, Inc.
1530 Wilson Boulevard
Arlington, Virginia 22208-2406


Dear Sirs:

                  This  firm has acted as  counsel  to Hagler  Bailly,  Inc.,  a
Delaware  corporation  (the  "Company"),  in connection  with its  registration,
pursuant to a  registration  statement on Form S-8 filed with the Securities and
Exchange  Commission  (the  "Commission")  on or  about  the  date  hereof  (the
"Registration  Statement"),  of 2,573,679 shares (the "Shares") of common stock,
$.01 par value per share, of the Company (the "Common Stock"), issuable upon the
award of shares of Common Stock  conditioned  upon the  attainment  of specified
performance goals or other factors  ("Restricted Stock") or upon the exercise of
options granted or to be granted  pursuant to the Company's  Employee  Incentive
and  Non-Qualified  Stock Option and  Restricted  Stock Plan (the "Plan").  This
letter is  furnished to you pursuant to the  requirements  of Item  601(b)(5) of
Regulation   S-K,  17  C.F.R.   ss.229.601(b)(5),   in   connection   with  such
registration.

For purposes of this opinion  letter,  we have examined  copies of the following
documents.

                  1.       An executed copy of the Registration Statement.

                  2.       The Amended and Restated Certificate of Incorporation
                           of the Company as certified by the Secretary of State
                           of the  State of  Delaware  on June 8,  1998,  and as
                           certified by the Secretary of the Company on the date
                           hereof  as  then  being  complete,  accurate  and  in
                           effect.

                  3.       The Bylaws of the Company,  as amended,  as certified
                           by the Secretary of the Company on the date hereof as
                           then  being  complete,  accurate  and in effect  (the
                           "Bylaws").

                  4.       A copy  of the  Plan  as  adopted  by  the  Board  of
                           Directors of the Company and the  stockholders of the
                           Company,  and as  certified  by the  Secretary of the
                           Company on the date  hereof as then  being  complete,
                           accurate and in effect.

                  5.       Resolutions  of the Board of Directors of the Company
                           adopted  at  meetings  held  on  December  11,  1996,
                           January 17, 1997 and March 11, 1997 and by  unanimous
                           written  consent on May 17,  1995,  December 31, 1996
                           and January 27, 1998,  as certified by the  Secretary
                           of the  Company  on the  date  hereof  as then  being
                           complete,  accurate and in effect, relating to, among
                           other things, the approval of the Plan and amendments
                           thereto and the filing of the Registration Statement.

                  6.       Resolutions  of  the   stockholders  of  the  Company
                           adopted at  meetings  on April 26, 1996 and March 11,
                           1997, as certified by the Secretary of the Company on
                           the date hereof as then being complete,  accurate and
                           in effect,  relating  to,  among  other  things,  the
                           approval of the Plan and amendments thereto.

                  We have not, except as specifically identified above, made any
independent  review or investigation of factual or other matters,  including the
organization,  existence,  good  standing,  assets,  business  or affairs of the
Company,  or its subsidiaries or of any other matters. In our examination of the
aforesaid  certificates,  records and documents, we have assumed the genuineness
of all signatures,  the legal capacity of natural  persons,  the authenticity of
all documents submitted to us as originals,  and the authenticity and conformity
with the original  documents  of all  documents  submitted  to us as  certified,
telecopied,  photostatic, or reproduced copies. We have assumed the authenticity
and accuracy of the foregoing  certifications of corporate officers, on which we
are relying, and have made no independent investigations thereof.

                  We have not, except as specifically  identified  herein,  been
retained or engaged to perform, nor have we performed, any independent review or
investigation  of  any  statutes,  ordinances,  laws,  regulations,  agreements,
contracts,  instruments, or corporate records to which the Company or any of its
property may be a party or may be subject.  This opinion  letter is given in the
context of the foregoing.

                  This  opinion  letter is based as of  matters of law solely on
the  applicable  provisions of Delaware law, and we express no opinion as to any
other laws,  statutes,  rules,  regulations  or  ordinances,  including  without
limitation any federal or state tax or securities laws or  regulations.  We note
hat our firm only  requires  lawyers  to be  qualified  to  practice  law in the
District of Columbia, Virginia, or Maryland.

                  Based upon,  subject to, and limited by the foregoing,  we are
of the opinion that the Shares,  when issues and  delivered in the manner and on
the terms  contemplated  in the  Registration  Statement  and the Plan (with the
Company  having  received the  consideration  therefor,  the form of which is in
accordance  with  applicable  law),  will be  validly  issued,  fully  paid  and
non-assessable.

                  We assume no  obligation  to advise you of any  changes in the
foregoing  subsequent  to the  delivery of this  opinion.  This opinion has been
prepared solely for your use in connection  with the filing of the  Registration
Statement  on the date of this  letter,  and should not be quoted in whole or in
part or  otherwise  be  referred  to,  nor be  filed  with or  furnished  to any
governmental agency or other person or entity, without the prior written consent
of this firm.

                  We hereby  consent to the filing of this opinion as an exhibit
to the Registration Statement.  Nothing herein shall be construed to cause us to
be considered  "experts"  within the meaning of Section 11 of the Securities Act
of 1933, as amended, or the rules thereunder.

                                                     Very truly yours,

                                                     /s/ HOGAN & HARTSON L.L.P.

                                                      HOGAN & HARTSON L.L.P.