* Dollar hit after some polls show Trump leading Clinton
* Dollar hits more than 3-week lows vs euro, yen, franc, sterling
* Mexican peso at weakest in more than a month vs dollar
* Fed awaited, but politics seen overshadowing fundamentals (Updates prices, adds comments; changes byline, dateline, pvs LONDON)
By Sam Forgione
NEW YORK, Nov 2 (Reuters) - The U.S. dollar hit its lowest level in more than three weeks against the euro, yen, Swiss franc and sterling on Wednesday on continued nervousness about a potential victory for U.S. Republican presidential candidate Donald Trump next week.
Investors are rethinking long-held bets on a Nov. 8 victory for Democrat Hillary Clinton. Clinton held a 5 percentage point lead over Trump, according to a Reuters/Ipsos opinion poll released on Monday, but some other polls showed her Republican rival ahead by 1-2 percentage points. dollar index .DXY , which measures the greenback against a basket of six major rivals, fell about 0.4 percent to 97.26, its lowest since Oct. 11. The Mexican peso tumbled to a more than one-month low against the greenback of 19.4295 pesos MXN= per dollar on fears of a Trump victory.
Markets' assumption in the past month has been that the dollar would fall if Trump won. Clinton is viewed as the candidate of the status quo, while there is greater uncertainty over what a Trump victory might mean for U.S. foreign policy, international trade and the domestic economy.
"There is a huge amount of unknown unknowns around Trump," said Richard Franulovich, a senior currency strategist at Westpac Banking Corp in New York. "That uncertainty is obviously anathema to markets."
The euro EUR= rose about 0.6 percent against the dollar to $1.1115, its highest since Oct. 11. The dollar sank 1 percent against the yen JPY= to 103.10 yen, its lowest since Oct. 10. The dollar plunged about 0.6 percent against the Swiss franc CHF= to 0.9695 franc, its lowest in roughly a month.
The Mexican peso suffered MXN= a more than 1-percent drop against the dollar for a second straight day. A possible Trump victory has been viewed as a key risk for the Mexican currency given the candidate's promises to clamp down on immigration and rethink trade relations.
"People are pricing in higher odds" of a Trump victory, said Win Thin, global head of emerging market currency strategy at Brown Brothers Harriman in New York.
The Fed ends a two-day meeting on Wednesday and is due to issue a statement at 2 p.m. ET (1800 GMT) that is widely expected to open the door, on economic grounds, to a hike in interest rates next month. A number of analysts said, however, that might prove irrelevant in the context of the election.