The 1990s, the 20th century, the second millennium--they all come to an end Friday night. Much attention is being paid.

That's fine. But if you're a taxpayer--and most of us are--Dec. 31 is important for another reason: It's the deadline for most maneuvering to reduce 1999 taxes.

Congress over the past dozen or so years has cut way back on taxpayers' wiggle room, wiping out or sharply restricting such tried-and-true devices as selling short against the box to defer gains on stock sales. At the same time, lawmakers have left the alternative-minimum-tax ceilings in place so that every year more taxpayers have to worry about being caught by the AMT.

Still, for taxpayers who itemize and those who have some flexibility on when they receive income, these last few days are an opportunity to review the bidding and maybe make a change or two to save money.

Until recently, the conventional wisdom of year-end tax planning was to defer income and accelerate deductions. That was reasonable. Lowering taxes today gives you the use of the money tomorrow, so you end up better off even if you ultimately have to fork it over to the government a year from now.

But the explosion of ceilings, thresholds and other limits has made things too complex to rely on rules of thumb. For example, deferring income until after Dec. 31 could propel you past the point where your deductions start phasing out next year. Likewise, retirees using that strategy could cause their Social Security benefits to be taxed at a higher level.

Conversely, shifting deductions into this year could trigger the AMT, possibly wiping out the benefits from the deductions this year and next. The AMT could raise this year's taxes enough to eliminate the deductions' benefit, while claiming them this year would mean you couldn't claim them next year when you might get the full benefit.

At the same time, these traps can ensnare taxpayers who don't try anything fancy, just because in the ordinary course of things their income or deductions pass some threshold.

In fact, the AMT, originally designed to prevent rich people from escaping income taxes through the use of tax "preferences" (often called loopholes), has evolved into a serious threat to the upper middle class. Not long ago, a family with an adjusted gross income of about $83,000 and a large number of children was found liable for the AMT even though they hadn't employed anything that normally would be seen as a loophole.

The AMT is both an economic and a paperwork headache.

It imposes a flat rate of 26 percent on income below $175,000 and 28 percent on income above $175,000. Taxpayers are required to pay it if their AMT tax--a tax calculated after backing out various "loophole" deductions such as state income and local property taxes and personal exemptions and including things such as interest on certain tax-exempt bonds--exceeds their regular tax.

That means doing two sets of calculations even if it turns out you don't have to pay it.

There is one piece of good news about the AMT, however. Congress at the last minute did restore a provision that protects several family-oriented tax credits, such as the child-care credit, from the AMT. That protection had been in the law for 1998 but had expired.

So--what to do between now and Friday?

Begin by at least eyeballing your tax situation, including, if you have a lot of deductions, a rough cut at the AMT to see if it's going to be a threat. If you expect your tax rate next year to be about the same as this year's, then you should consider accelerating any deductions you can.

You can do this by prepaying such items as the last installment of state and local estimated income taxes, real estate taxes and charitable donations you had been planning to make.

Deferring income is tough for salaried workers, but if you are expecting a year-end bonus, you may be able to persuade your employer to put it off a week, thus causing it to be reported as 2000 income.

Next, look at other income you may have. For example, if you have substantial capital gains this year, you can consider selling losers, if you have any, to offset those gains. In addition, such losers can be used to offset up to $3,000 of ordinary income as well.

Unfortunately for investors who would like to lock in a gain this year but defer recognition until 2000, Congress has sharply tightened the rules on selling short against the box.

This strategy involved borrowing securities equivalent to the ones you have and selling them now, and then delivering the ones you own to repay the loan next year. In the past you could defer recognition of the income until the whole deal was complete, but now in many cases the income is recognized when you enter a short position holding essentially identical securities. It's still possible to use this strategy, but check carefully before trying it.

Other things you can do include:

Bunching certain deductions. Both medical expenses and miscellaneous business expenses become deductible only when they exceed certain thresholds. If you have had or are expecting substantial expenses of these sorts, check to see if paying those that are outstanding would enable you to get a deduction this year, or if putting them off would create a deduction next year. If you're married and the expenses are attributable to one spouse, also see if filing separately would give that spouse a worthwhile deduction.

Giving appreciated securities to charity. If you intend to make a gift to a charity anyway, donating appreciated securities you have held more than one year allows you to write off the full current value, subject to certain limitations, so you're often better off doing that than selling the securities, paying tax and then giving the cash.

Note that if you donate securities you have held less than a year, your deduction is the lesser of what you paid or current market value. With such a donation you would lose either the benefit of the appreciation or a loss that you could have deducted.

Setting up a Keogh retirement plan if you have self-employment income. The deadline is Dec. 31 for setting up the plan, though the money doesn't have to be contributed until the due date of your return.

Making a gift of up to $10,000 ($20,000 for a married couple) to a child or grandchild. Such gifts don't reduce your income tax, but they are not subject to gift taxes and can be used to move money out of your estate into into the hands of younger family members tax-free.

Looking Ahead for Taxes

In trying to decide whether income and deductions are better recognized in 1999 or 2000, it's helpful to know what tax brackets are likely to be. Brackets are adjusted each year for inflation. Here are the 2000 brackets for singles and married couples filing jointly, as calculated by the Research Institute of America.

Single individuals (other than heads of households and surviving spouses)

If taxable income is:

The tax is:

Not over $26,250

15% of taxable income

Over $26,250 but not over $63,550

$3,937.50 plus 28% of the excess over $26,250

Over $63,550 but not over $132,600

$14,381.50 plus 31% of the excess over $63,550

Over $132,600 but not over $288,350

$35,787.00 plus 36% of the excess over $132,600

Over $288,350

$91,857.00 plus 39.6% of the excess over $288,350

For 1999, the 28%, 31%, 36% and 39.6% rate bracket changes occurred respectively at $25,750, $62,450, $130,250 and $283,150 of taxable income.

Married individuals filing joint returns and surviving spouses

If taxable income is:

The tax is:

Not over $43,850

15% of taxable income

Over $43,850 but not over $105,950

$6,577.50 plus 28% of the excess over $43,850

Over $105,950 but not over $161,450

$23,965.50 plus 31% of the excess over $105,950

Over $161,450 but not over $288,350

$41,170.50 plus 36% of the excess over $161,450

Over $288,350

$86,854.50 plus 39.6% of the excess over $288,350

For 1999, the 28%, 31%, 36% and 39.6% rate bracket changes occurred respectively at $43,050, $104,050, $158,550 and $283,150 of taxable income.

SOURCE: Research Institute of America