The uncertainty over looming tax increases is starting to affect both investing and corporate decision-making.

The economy remains the biggest factor in many investors' and businesses' decisions. But worries over whether Congress will extend some or all of the expiring Bush-era tax breaks are emerging as an important one.

Stock prices of utilities, for example, recently have appeared to be factoring in the possibility of significantly higher dividend taxes next year, several analysts say. Some companies are pumping up dividend payments this year to beat the possible 2011 tax increase, and their shares have rallied.

Small-business owners say unease about tax policy, along with the economy, has led them to hold off on hiring and investment. And many advisers are encouraging well-to-do clients to sell appreciated assets to avoid higher capital-gains taxes.

Congress hasn't decided how to address the tax cuts from the George W. Bush administration, which are set to expire Dec. 31. President Barack Obama proposes to allow taxes on dividends and capital gains to rise to 20% from the current 15% for higher earners, defined as families with incomes of more than $250,000. But many Democratic lawmakers want to let dividend tax rates, along with ordinary income rates, rise next year for higher earners to as much as 39.6%.

A senior House aide said late last month that Democratic leaders hadn't decided yet whether to end the current rates on dividends and capital gains for higher earners, or to extend them for everyone. Republicans are largely united in calling for a complete extension, although House GOP Leader John Boehner on Sunday signaled a measure of flexibility. If Congress takes no action, investment taxes would go up virtually across the board.

The broadest impact of higher investment taxes could come on financial markets. But analysts and economists differ over the likely effect.

A July analysis by Barclays Capital suggested that increasing taxes on investment income, as many Democrats advocate, could trim about 9% off the S&P 500 index. Talley Leger, vice president of U.S. portfolio strategy for Barclays Capital, called it "a potential headwind for stocks for the next couple of years."

A 2005 study by three economists at the Federal Reserve, looking back at the market response to the 2003 Bush tax cuts on dividends, concluded there wasn't a significant impact on overall stock values.

Alan Auerbach, a professor at the University of California at Berkeley who also has studied the effect of the Bush tax cuts, said the evidence suggested that repealing the changes probably would produce a "small negative effect" on financial markets.

Citigroup Global Markets forecasts that if all the proposals to raise dividend tax rates take effect for higher earners, investors could pay an additional $39 billion in taxes in 2013.

"That's a big effect, and probably a bit bigger than some market participants believe," said Steven Wieting, U.S. economist at Citigroup Global Markets.

There are signs that tax concerns have been affecting a range of transactions on the ground. Analysts say spreads between utility-stock dividend yields and yields on some other securities recently have reflected expectations of a top dividend tax rate in the low-30% range.

"The stocks could initially fall if dividend tax rates reset to marginal rates, but we don't think it will be permanent," said Dan Eggers, a utility equity research analyst at Credit Suisse Group in New York.

Some companies are squeezing in big dividends before year's end. In anticipation of its conversion to a real-estate investment trust, Weyerhaeuser Co. plans a $5.6 billion accumulated-earnings dividend payout this year, most of it in the form of stock. Pharmaceutical company Warner Chilcott PLC has arranged to borrow more than $2 billion to make an extraordinary dividend payment of $8.50 a share to shareholders.

While dividends are getting most of the attention, wealthy investors also are facing big incentives to realize capital gains by selling assets. "We advise people that if they have gains to take or oversize positions that need to be diversified, sell them before the end of the year, rather than wait and pay higher taxes," said Sam Katzman, chief investment officer at Constellation Wealth Advisors in New York.

Small-business owners, especially older ones, also face tax incentives to sell soon. "If someone is planning on selling a business, they should do it now," said Chris Walters, an executive vice president based in Pasadena, Calif., at CitizensTrust, the wealth management arm of Citizens Business Bank.

Some are hesitating, hoping for higher prices in the future. And business owners who sell now can face risks, because of the way such deals may be structured. Chris Hesse, head of the tax practice at LeMaster Daniels in Spokane, Wash., said a client in his early 60s sold his remaining shares in a business in a 10-year installment deal, and chose to pay all the tax at once this year, in anticipation of higher rates in the future. That looks like a smart strategy—unless the buyer can't make the future payments.

The prospect of higher taxes in 2011 and beyond also could be weighing on business owners' operational decision-making. In its July survey of small-business owners, the National Federation of Independent Business found that 22% of small businesses said the most important problem they faced was taxes, up from 19% a year earlier. More businesses—29%—identified poor sales as their No. 1 problem, but that was down from 34% a year earlier.

Democrats say that less than 3% of small-business owners would be affected by changes in tax rates for high earners. Republicans say that figure is affected by the large numbers of taxpayers who report small amounts of income from side businesses. Republicans focus instead on the large amount of small-business income that would be affected by the rate hikes, which they say is about half of all such income.