As the season approaches for yearend tax planning, investors face the possibility that some standard, time-tested strategies might not work so well this year.

In normal circumstances, the main idea in yearend maneuvering for tax purposes is to minimize the tax liability from investments you would incur for the current year's tax return.To do that, you could use any one of several techniques for postponing realization of capital gains until the new year arrives.

In addition, you might sell an investment that has performed poorly before yearend, taking a loss to offset profitable sales made earlier in the year or to reduce your other income by as much as $3,000.

Advisers on tax matters have traditionally urged their clients to take these steps early, so as not to be caught in the late-November and December rush.

But thanks to the elections, the federal budget deficit and the possibility of additional changes in the tax code before too long, many of the experts are hesitating to make the usual recommendations right now.

As Standard & Poor's Corp. put it in its advisory publication The Outlook:

"Keep in mind that shifting investment gains forward to 1989 could be the wrong move if tax rates rise next year, a possibility that certainly can't be ruled out.

"On the other hand, the next tax hike could come in a package that would lower capital gains tax rates."

Adds William Brennan, a Valley Forge, Pa., adviser on tax and investment planning, "Ingrained in our subconscious is the notion we must delay income taxes as long as possible.

"1988 may be the year to purge ourselves of this preconception - the 28 percent tax rate won't last forever."

The idea of postponing tax liabilities rests on a solid foundation known as the time value of money. The longer you can legally put off the time of reckoning, the longer you have the use of the money and its earning power.

Many long-term investment strategies are geared to delaying taxes until after you retire, when you presumably fall into a lower tax bracket than you occupied in your peak earning years.

The problem is, the virtues of tax postponement come into question when you do not know what future tax rates will be.

No matter what is said during the presidential election campaign, many financial observers believe "revenue-raising" proposals will be made next year because of the need, mandated by law, to narrow the federal budget deficit.

Nevertheless, some observers say, there is a case to be made for waiting longer than usual to decide on 1988 tax strategies - if you think, or hope, that the rest of the campaign and the results of the Nov. 8 elections will help to clarify the tax outlook for next year and beyond.

No matter what the future may hold, there is a natural human tendency to want to reduce the current year's tax burden, if only for the emotional satisfaction that comes with a refund in the spring.

For investors planning to sell losing investments before yearend, experts offer the reminder that they must avoid what the Internal Revenue Service calls a "wash sale."

If you sell an investment, and repurchase it within 30 days (either before or after) the date of the sale, the loss from the sale does not qualify for any deduction.

In the unusual environment that prevails this year, tax advisers agree, one old precept still applies: While tax planning is important, short-term tax considerations should never become so paramount in your mind that you permit them to lead you astray from your long-term plans and goals.