Not to be a wet blanket, but now that Labor Day is past, it’s time for investors to start thinking about year-end tax planning.

Too early? Not really. Hurricane Katrina, the war in Iraq, the Federal Reserve’s interest-rate policy, spiking fuel prices, shifting exchange rates. … These wild cards could cause some dramatic and unpredictable moves in the financial markets by the end of the year. It’s only prudent to have a tax strategy in place so you’re ready to move as conditions change.

I’ll have lots to say on the subject as we get into the fall. But for now, here are some of the key things to keep in mind:

¢ Basic strategy. Generally, it’s best to postpone tax bills as long as possible. That way, the money you’ll eventually use to pay taxes stays in your accounts longer. Hopefully, it will grow.

During some recent years, tax cuts have clouded this issue, but that’s not the case this year, as the key tax rates will be the same in 2006 as they are this year.

¢ Nurturing the portfolio. This should go on all the time, but year-end tax issues are an extra reason to rethink your holdings.

Of each investment, ask, “Would I buy it today at the current price?” If you would not, it’s a good candidate for a sale, whether it’s gone up or down.

Because the major stock indexes have not made major moves this year, many investors are probably neglecting this chore. That’s unwise – calm in the broad market can mask lots of turmoil below the surface.

Even if a stock or fund share is selling for the same price it was a year ago, its prospects may have changed significantly. Many energy stocks have done very well, for example, and investors should think about whether it’s time to cash in.

¢ Selling winners. You may want to sell a money-making stock or mutual fund because you don’t think it will go up much more, because too much of your portfolio is now tied up in it or because another investment is more promising.

If the investment is likely to collapse, or if the alternative is about to soar, sell now, regardless of the tax issues.

But if you think you have time, consider holding the investment until you’ve had it at least a year. That way, your profit will be taxed at the maximum long-term capital gains rate of 15 percent, rather than a short-term rate as high as 35 percent.

Also consider postponing the sale until after the end of the year to delay the tax bill a year.

¢ Selling losers. With these, it’s almost always best to sell sooner rather than later. It’s better to move your money to a more promising investment – and there’s rarely a tax benefit in delaying a sale.

The loss can be used to offset profits from other investments, thus reducing the capital gains tax on winners. If investment losses are greater than your gains, they can be used to offset up to $3,000 in ordinary income, reducing your income tax. Losses also can be carried forward to offset capital gains or income in future years.

¢ Partial pruning. Investors often want to simply reduce, rather than eliminate, their stake in a particular holding. This is simple if you bought all the shares at the same time.

But suppose your vast holdings in Widget Corp. stock were built up over the years, with various prices paid for different shares? In that case, use the rules described above to determine which shares to sell.

In general, sell the ones purchased at the highest prices. If the investment was a winner, these will show the smallest profit and, hence, trigger the smallest tax bill. Or they might be the ones with the biggest losses, giving you the biggest tax benefit.

To sell specific blocks of shares, you must designate them before the sale, in writing. Your broker or mutual fund company can tell you how.