The decline in U.S. stocks has been particularly noticeable in companies that pay big dividends. Barclays Capital pointed out in a research note that two of the three sectors hit hardest in the first half of November, utilities and telecommunications, had the highest dividend yields. Tax rates are scheduled to go up far more on dividends in January than on other income.

Not only that, but history suggests that if dividend taxes are raised, fewer American companies will pay dividends and instead will use their earnings in other ways. Data from S.&P. Dow Jones Indices show that the number of companies paying dividends held fairly stable during periods when the highest tax rate was the same on dividend income as on long-term capital gains, as in the past decade or in the mid-1980s through late 1990s. In between those periods, when dividends were taxed at higher rates than capital gains, the number of dividend-paying companies fell sharply.

That might not happen this time around, a study by WisdomTree Investments, a provider of exchange-traded funds, suggests. The study notes that dividend payments as a proportion of corporate earnings have been declining for decades, so the effect of higher tax rates could be muted.

American investors worried about rising tax rates might consider selling stocks in which they have large unrealized gains, investment advisers say. After the selling wave in early November, however, and with the outcome of fiscal cliff talks in Congress still unknown, it is hard to gauge whether that would be better than hanging on until 2013 or not acting at all.

“Things could be radically different a week or two from now,” said Adam von Poblitz, head of estate planning for Citi Private Bank. The uncertainty “has put a lot of clients in a state of paralysis,” he observed. “If people knew that XYZ were going to happen, they might not like it, but they would know how to proceed.”

One tactic for well-off individuals that Mr. von Poblitz considers a surer thing involves giving money away rather than making it. While attention has been focused on income and investment taxes, he notes that the tax rate on gifts is also due to rise in 2013, to 55 percent from 35 percent, payable by the giver. Perhaps more important, the lifetime amount that can be given tax-free is due to fall to $1 million from $5.12 million.