Sec. 168. (a) Until such  time as an applicable  implementation
plan  is ineffect for any area, which plan meets the requirements
of this  part to prevent significant deterioration of air quality
with respect  to any air pollutant,  applicable regulations under
this  Act prior to enactment of  this part shall remain in effect
to  prevent significant deterioration of air  quality in any such
area for  any  such pollutant  except  as otherwise  provided  in
subsection (b).
  (b) If any regulation in effect prior to enactment of this part
to  prevent significant  deterioration  of air  quality would  be
inconsistent with  the  requirements of  section 162(a),  section
163(b) or section 164(a),  then such regulations shall be  deemed
amended so as to conform with such requirements. In the case of a
facility on which construction  was commenced (in accordance with
this  definition of "commenced" in section  169(2)) after June 1,
1975, and prior to the enactment of the Clean  Air Act Amendments
of 1977, the  review and permitting of such  facility shall be in
accordance with the regulations for the prevention of significant
deterioration in effect prior  to the enactment of the  Clean Air
Act Amendments of 1977.
[42 U.S.C. 7478]