The poll conducted for the St. Louis Post-Dispatch and KMOV shows Romney with 51 percent support, compared to 42 percent for Obama.
The survey also shows Democratic U.S. Sen. Claire McCaskill trailing any of her three likely Republican challengers. In the Republican Senate primary, the poll found 33 percent supported businessman John Brunner, 27 percent for former state Treasurer Sarah Steelman and 17 percent for Congressman Todd Akin. Nineteen percent remained undecided.
The poll also showed Democratic Gov. Jay Nixon leading his potential Republican challengers.
Mason-Dixon Polling and Research surveyed 625 registered Missouri voters by telephone from July 23-25. The poll had a margin of error of plus or minus 4 percentage points.