Is a lump sum falling your way? Advisers agree on where to put it

How nice. You never expected such a generous inheritance. Now that you have this lump sum, however, what's to be done with it? Financial windfalls like this are not so unusual. They come from everyday events: insurance or divorce settlements, capital gains from selling a business or real estate, and pension plans at retirement.

Even people who expect to acquire a large pool of cash don't always have plans for it, let alone those who wake up and find themselves quite a bit wealthier than they were the day before. Eventually, they have to come up with an overall investment plan molded to individual needs and goals. But what's to be done in the meantime? Where do you put thousands of dollars while figuring out what you really want to do with it?

The vote among four financial experts contacted here is unanimous: For many people, the best parking space for a chunk of cash is a money market fund.

''It gives you safety, it gives you liquidity, and there are no (early withdrawal) fees,'' says James Sullivan, a certified financial planner in Acton, Mass., a Boston suburb. With check-writing and easy transfer from money funds to your personal bank account, it's one of the most liquid investment instruments around. Don't, Mr. Sullivan warns, just put the sum in a NOW account or passbook savings account, where interest rates are almost four percentage points lower than the going money-market rate. He also says it isn't necessary to diversify among money market funds, because their safety factor is high.

Not all money funds are equals, though. Look for the ones that credit interest daily. Also, some states, such as Massachusetts, have a lower tax rate for investment income coming from money market deposit accounts offered by in-state banks. (And remember that an insured money market deposit account, offered by a bank, is not the same thing as a money market mutual fund, although an MMDA offers interest almost as good.) Then there are tax-exempt funds, which pay out interest of about 5 percent rather than the going rate of 9.5 percent for most other money funds.

The thing to underline when first investing a windfall is short-term, emphasizes Robert Martel, a certified financial planner heading his own firm in Lexington, Mass. ''You want flexibility, but you don't want to sit on a money fund too long, because after taxes you'll get the inflation rate, if just that, '' he explains. ''Say you are getting 9 percent on the money fund, you are in a 50 percent tax bracket, you will probably net around 4 percent. That just doesn't hack it.''

Tax considerations are important when dealing with windfalls. First, one has to consider whether the money is tax free.

Inheritances, insurance claims, and most judgments are. Divorce settlements and pensions are a mixed bag. Capital gains, of course, are taxed, either at a short-term rate (where the maximum federal tax is 50 percent) or at a long-term rate. The long-term rate applies to investments held for at least a year (the maximum federal tax is 20 percent). The general rule for selling a home is that the profit is tax-free for two years, if by the end of that time you buy another primary residence for at least as much as the selling price of the first home.

Then, remember that the investment income from this windfall is likely to catapult you into a higher tax bracket.

''You must make sure you understand how much you are taking home from interest income and what effect it will have on filing taxes the following year, '' says Elizabeth Foster, an investment executive at Moseley, Hallgarten, Estabrook & Weeden Inc., in Cambridge, Mass.

To figure this out, refer to this year's tax table, estimate your interest income from the money fund, and do a quick calculation of tax payments. Then try it for other short-term investment vehicles: Treasury bills, tax-exempt money funds, certificates of deposit.

If you are in the 40- to 50-percent tax bracket and have come upon a major windfall, it would be worth it to look into tax-free, short-term investments - municipal bonds, tax-exempt money funds, or government securities (free from state tax only). For instance, says Miss Foster, suppose you are in the 45 -percent tax bracket or above (filing jointly or as a single) and you tie up money for one year in a municipal bond paying 6 percent interest. On a federal tax basis alone, you would have to be earning 10.9 percent in a taxable money fund to net the same income as you would from the municipal bond.

''Depending on the state, you can make an even stronger case to be in a tax-exempt municipal bond in that state, because you will also get state tax exemption on the interest income,'' she says.

When you are talking about a windfall of half a million dollars or more, then it pays to look outside the money market account - even for the short term. ''One percent can make a lot of difference,'' says Irma ten Kate, an assistant vice-president at Kidder, Peabody & Co. She recommends keeping a certain amount liquid, in a money fund, but also looking at less flexible investments such as three-month Treasury bills, certificates of deposit, and commercial paper.

''You have to keep in mind that this is temporary,'' says Beth Foster. ''Just how complicated do you want this to be? You'll want to be able to get your money as easy and as fast as possible.'' That's why she recommends the money fund.