Washington, D.C. ? Actor and former Sen. Fred Thompson leads the Republican presidential field in Nevada even though he has not declared his candidacy, according to a new poll made available to McClatchy Newspapers and NBC News.

The poll by Mason-Dixon Polling and Research showed Sen. Hillary Rodham Clinton with a substantial lead over her Democratic rivals.

Nevada could have an influential role in selecting the presidential nominees in 2008 because the state will hold its nominating caucuses on Jan. 19 – five days after Iowa and three days before New Hampshire’s primary.

Thompson’s strength in Nevada, which mirrors his recent surge in national polls, underscores his potential to shake up the Republican race if he decides to run. The former Tennessee senator is recruiting a campaign staff and testing his appeal as a candidate.