Investors should begin to take advantage of the super high interest rates that currently are available in the marketplace. It has become obvious that the Federal Reserve means business, and its tightening of the availability of credit has pushed short-term rates close to their all-time peaks. Long rates hit their peaks two weeks ago and have declined slightly since then.

Bill Donoghue's recent "Money Letter" pointed out that Americans forfeited approximately $35 billion in interest last year by keeping their funds in investments that paid low rates of interest. Consequently these investors now have a second, or is it a third chance to rectify last year's error.

It would appear that the Federal Reserve miscalculated in their strategy since they intended to allow rates to decline some in March. Probably everyone erred because very few people realized the true strength of the economy. Only on Tuesday -- when the growth of the Gross National Product for the first quarter was revised upwards to 8.4 percent from 6 1/2 percent -- was the underlying vigor of our economy appreciated. This latent strength in the economy also tells us why the money supply has been growing. Furthermore, the GNP price deflator, a broader measure of inflation, also was revised up, from 7.8 percent to 10 percent. Certainly not good news.

The bottom line according to Peter Gordon, the municipal bond expert of T. Rowe Price is, "that the Fed must remain restrictive until they show that they can get control of the money supply and change inflationary expectations or until there is a definite weakening in the economy." This means the market will endure some volatile activity during the next several weeks, moving up and down on economic and money supply news dictating market direction.

Because of the uncertainty of the economy and inflation and the volatility of the markets, conservative investors should not extend longer than five years and a healthy cash position also should be maintained.

Tax-exempt money market funds are returning between 6 1/2 percent and 7 1/4 percent. Short-term notes due within one year are returning between 7 1/2 and 8 3/4 percent. Three year, tax-exempt, A-rated, pollution-control revenue bonds are returning 9 percent.

Taxable money market funds are returning 15 percent, and the new two-year Treasury note is returning 15 1/4 percent.

Also, four major brokerage houses sponsored in a two-week period $1.1 billion of six-month, taxable-unit investment trusts with yields ranging from 16 to 17.49 percent. These trusts have been coming to market at the rate of one to two per week. Because of the demand they are generally all sold within two hours. Merrill Lynch, the senior manager, expects to continue to bring these to market as long as the demand exists and suggest investors express interest to the sponsors in advance of the offerings. The other sponsors are Dean Witter Reynolds, Bache Halsey Stuart and Shearson Loeb Rhoades. The cost is approximatly $1,000 per unit.

The Treasury will auction a five-year, five-month note on Thursday. It will be available in minimum denominations of $1,000 and probably will return 14 3/4 percent or higher.

E. F. Hutton will offer some time this week a Prince George's County, Md., floating-rate bond issue for the Potomac Electric Power Co. The coupon of this issue will change weekly, based on a formula pegged to the 90-day Treasury bill or 30-year Treasury bond. The price of this type of tax-exempt has remained close to par despite price swings in the market.