IT'S fall, pumpkins are out, Thanksgiving is just around the corner, and the stock market is still hitting high terrains. That means it's time to get serious about - taxes.
For thousands of investors, the large run-up in stock prices during 1995 makes tax planning ''more important than usual,'' says Elda Di Re, a partner with the accounting firm Ernst & Young LLP.
For example, if you are now contemplating buying into a new mutual fund that has racked up substantial gains this year, ''you might want to wait'' until after the fund formally records a distribution of dividends to account holders during the next few weeks, Ms. Di Re says.
The reason: If you buy a fund now, and it pays a capital gain, you are in effect ''buying that dividend,'' just as though you had held the fund all year. Instead, check with the mutual-fund company and ask when the dividend will be declared. Wait until the next day to buy.
Persons who hold individual stocks that have posted especially impressive price gains might need to consider several tax alternatives, says Mark Luscombe, an attorney and principal tax analyst with CCH Inc. in Riverwoods, Ill. CCH is a provider of tax information and software.
Congress is currently considering retroactively lowering the capital-gains rate, which is now 28 percent and applies to securities held longer than one year. If you have an individual stock that has done very well and you want to lock in the price gain, you face a choice. You could sell now, Mr. Luscombe says. If Congress lowers the capital-gains rate and makes it retroactive to 1995, you come out ahead, with a lower rate. Or you could wait until next year to sell, hoping Congress lowers the rate.
But what if the market dips? There goes your price gain. According to Luscombe, you have another alternative. You could ''sell short against the box.'' That lingo means you defer the tax consequence for a year. Here's how: You sell ''short'' an equal number of the same shares that you now own. The sale is set for a specified future date, sometime in 1996, and the sales price is ensured - such as at the current market price of the stock. At the future time in 1996, you deliver the shares. Thus, the trade is considered to have occurred in 1996, not 1995. You have locked in your price gain, but deferred the tax until next year. The tax bill will not come due until April 15, 1997.
If you are selling off some securities from multiple lots purchased over time - that is, for example, from groups of 100 shares or more - have your broker or mutual fund sell the shares from among your most recent purchases. That way, according to tax experts, you will have less gain.
If you have substantial assets in equities, you might find it financially advantageous to consult a tax attorney or certified public accountant regarding your tax consequences, Di Re says. Tax guides can be helpful. The new Ernst & Young Tax Savers Guide 1996 ($10.95) has, for the first time, an entire chapter on mutual-fund tax strategies.
Additional tax strategies:
* Marriage. If you are getting married before the end of 1995, you might want to rethink the date, according to Ernst & Young. That sounds rather unromantic! But if you both have high incomes, your combined tax may turn out to be higher - the so-called ''marriage penalty.'' Waiting until after Jan. 1 defers the tax to another year.
* Charitable deductions. The IRS has tightened rules. If you give $250 or more to any one charity, be sure to get a written acknowledgment. Your canceled check is not enough. Don't forget to take a deduction on clothing donations. To determine how much you can deduct on individual clothing items, call 800-875-5927 and ask for the booklet ''Cash - For Your Used Clothing.'' It costs $17.95 through Dec. 31.
* Bunching. One important tax-saving step, according to Ernst & Young, is to group deductions into years where expenditures are high. Medical/health expenses are only deductible if they exceed 7.5 percent of your adjusted gross income (AGI). So if you are planning major dental work, or need new glasses, bunch the work and purchases into one tax year to try to exceed the 7.5 percent limitation. That also applies to miscellaneous deductions. They can only be deducted if they are greater than 2 percent of your AGI.
* Tax-deferred accounts. Dollar contributions can be put into a 401 (K) or 403 (b/c) retirement plan through Dec. 31. Funds can go into an Individual Retirement Account through April 15, 1996. A Keogh plan, for self-employed persons, has to be opened by Dec. 31, but contributions can be made through April 15, 1996.
Finally, if you can, experts say, prepay the January mortgage interest to boost your deductions, if you have high earnings this year. And if you are getting a salary bonus, have payment deferred until next year.