NEW YORK, July 25 (Reuters) - A quarter of rich U.S. investors are so concerned that the U.S. presidential race will hurt share prices that they are considering pulling out of the stock market entirely, according to a survey by UBS AG Wealth Management Americas.

Five percent of the 2,300 mostly high net worth investors surveyed said they had already converted all of their U.S. stock holdings to cash, according to survey of investors in early June.

"Investors really see this (election) as a watershed event," said Sameer Aurora, UBS head of client strategy for Wealth Management Americas. "They are extremely concerned about the outcome of the election on their own personal financial wellbeing."

Unpredictable and sometimes fiery rhetoric from candidates in this year's election has given investors reason to worry. A tweet from presumptive Democratic nominee Hillary Clinton in September sent biotech stocks crashing.

Republican candidate Donald Trump has promised to dismantle financial reform laws, force Canada and Mexico to renegotiate the North American Free Trade Agreement and slap steep tariffs on Chinese and Mexican imports.

Investors have amassed the largest cash pile since 2001 and equity holdings are at a four-year low, a Bank of America gin> Merrill Lynch study found. The reticence is hampering profit margins at big banks, which make money off managing clients' assets.

The political leanings of the participants in the survey were evenly split between Republicans, Democrats and Independents.

The vast majority of respondents, approximately 84 percent, said their No. 1 issue was the economy, citing concerns over how each candidate would address stagnating wages, consumers' purchasing power and the well-being of future generations.

Despite consensus on the problem, investors split largely along party lines on how to fix the economy. Eighty-six percent of Republicans said balancing the budget would help, compared to 61 percent of Democrats and 78 percent of Independents.

Overall, 57 percent of investors said they were considering changing how their investments were allocated ahead of the election, and three out of give said they plan to discuss or have already discussed the election with their advisers.

The study did not ask investors which candidate they planned to vote for in November.

(Reporting By Elizabeth Dilts; Editing by Carmel Crimmins and Cynthia Osterman) ((elizabeth.dilts@thomsonreuters.com;)(646)(223-5063; Reuters Messaging: elizabeth.dilts.thomsonreuters.com@reuters.net))