force indexed search?

Is there a way to force postgresql to use indexing on a select statement containing "or"?


this SQL statement uses indexing...
  SELECT name, hsno, area FROM parc WHERE pin = '40-002' ;


This SQL statement uses sequential search...

  SELECT name, hsno, area FROM parc WHERE pin = '40-002' or pin = '40-106' or
    pin = '40-013' ;