A friend who worked in New York City's garment center used to say that his business had five seasons: Winter, spring, summer, fall and S-L-A-C-K. The investment business has a fifth season, too. It's called IRA, and it's B-U-S-Y.

IRA fever generally strikes about this time of year as people begin thinking about the April 15 deadline for filing their federal taxes and the need to find deductions quickly. Fortunately, making a $2,000 investment in an Individual Retirement Account is a fast way to get a $2,000 income tax deduction, a fact that encouraged 19.2 million people to establish IRAs in 1983.

With April 15 approaching, many people are scurrying to set up 1984 IRAs. Others are opening their 1985 IRAs to take advantage of the extra interest they can earn by putting in their money as soon as possible.

A study by T. Rowe Price, the Baltimore mutual fund company, says the timing of IRA investments can make a major difference in dollars accumulated. An investor who puts away $2,000 each Jan. 1 for 30 years at 10 percent interest will realize a total of $361,886. The same investor putting the same money away the following April 15 each year will earn only $319,548, a $42,338 gap.

On the theory that investment professionals -- brokers, financial planners and stock analysts -- are likely to be particularly careful when it comes to handling their own funds, we asked several professionals to tell us how they were investing their personal IRA money. They were generally candid about their choices and here is a summary of what they had to say:

* Carole S. Rollinson, manager of the Prudential-Bache office in Bethesda, favors a conservative approach and will put her $2,000 in a five-year certificate of deposit available from her firm. It will yield 11.45 percent and the twice-a-year interest payments will go into a Bache money market fund paying about 8 1/2 percent interest. However, she will manage a more aggressive IRA for her husband, Mark Rollinson, a lawyer, who wants to put his money into stocks. The stock they've chosen is MacNeal-Schwendler, selling at about $13.625 a share with a price-to-earnings ratio of 30. The firm is involved in computer-aided design and manufacturing.

* Robert F. Keller, financial management adviser at E. F. Hutton & Co., Bethesda, expects to put his 1985 IRA into the Franklin U.S. Government Securities Fund, a mutual fund made up of Ginnie Maes, guaranteed government securities issued by the Government National Mortgage Association (GNMA). Ginnie Maes represent shares in a pool of FHA and VA mortgages.

The Franklin fund currently yields 12.20 percent, but the yield can vary depending on interest rates. The fund also pays a lesser amount on the principal of the mortgages, which have an average life of 12 years, but this payment, too, can vary. Shares in the fund currently cost about $7 and will fluctuate, depending on the interest rate climate.

* E. Joseph West, vice president of investments at Drexel Burnham Lambert in Washington, is splitting his $2,000 IRA investment. Half will go into an aggressive equity fund, the Lord Abbett Developing Growth Fund, composed of stocks of small- to medium-size high-growth companies and currently selling for $9.25 a share. The fund charges an 8.5 percent commission. Prices of the shares will vary as the prices of the stocks in portfolio change. During the past five years -- with all dividends and capital gains reinvested -- the fund grew at a compound annual rate of 12.91 percent. The other half of West's IRA funds will go to Drexel Burnham's Fixed Income Trust Zero Coupon Series I, a zero-coupon corporate bond fund. Units currently sell for $16.45. They will mature at $28.77 a unit in 5.321 years, (June 1990) with a locked-in yield of 11.08 percent.

* Howard Taylor, senior account executive at Merrill Lynch in Washington, will put 75 percent of his 1985 IRA into the Keystone Mass. B2 Investment Grade Fund, a no-load (no commission) corporate bond fund currently paying 11.78 percent interest a year. Shares currently sell for $17.82 and will vary with long-term interest rates. The other 25 percent of Taylor's IRA money will go into Merrill Lynch Hubbard Income Properties, a real estate limited partnership that has a guaranteed 9 to 10 percent yield. The intended life of the partnership is five to 10 years. After the original investment is repaid with interest, investors get 85 percent of any profit on buildings that are sold by the partnership.

* Henry T. Donaldson, vice president at Julia M. Walsh & Sons Inc. (a division of Tucker Anthony & R. L. Day Inc.) of Washington, puts his faith in stocks and his clients' money into Fidelity Equity-Income Fund, a low-load fund (2 percent commission) that now yields about 7 percent annually. The fund is made up of blue-chip stocks, and strives for capital appreciation and for a yield that is better than the Standard & Poor's 500. Donaldson says the best way to handle IRA money is to put it into well-managed blue-chip portfolios because "they will consistently make money over a long period of time."

* Michael L. Mead, research director at Scott & Stringfellow, Richmond, says that because he is 32 years old, he can invest in aggressive stocks and wait for them to grow. He put previous IRA money into MCI Communications when it was $14 and watched it drop to $7.25. It has since moved up over $10 and Mead has faith it will go higher. "In an aggressive stock," he said, "I want to see a company that has a niche, a company that has a clear direction." For his 1985 IRA, Mead is considering an investment in Golden Nugget ($11.75) or Piedmont Aviation, ($34.875), an airline Mead has recommended to his firm's clients. For more conservative IRAs, he would consider PepsiCo ($48.125) and Royal Dutch Petroleum ($55).

* Marilyn W. Lowen, vice president at Laidlaw Adams & Peck Inc. in Rockville, believes that, at present, an investor can do better in a real estate income program than in mutual funds, where the risk is higher for a potentially smaller return. Her 1985 IRA will be invested in Consolidated Capital Institutional Properties II, a limited partnership that buys residential and commercial income-producing properties and pays a guaranteed 9 percent interest. After nine years, the investor's money is returned, along with 75 percent of any profit realized from the sale of the properties.

* Leslie J. Silverstone, senior vice president of Dean Witter Reynolds Inc. in Washington, put his 1984 IRA into the stock of a rival brokerage firm that looked like it had growth potential. He was right. The stock, which he'd rather not identify, is up about 40 percent. For 1985, he expects to put his $2,000 in Dean Witter's no-load Developing Growth Securities Fund, which seeks long-term capital growth by investing in rapidly developing companies. The current share price is $8.76.

As a general rule, E. F. Hutton's Bob Keller suggests, investors who are within 10 years of retirement should stay with fixed-income investments. These include zero-coupon Treasury obligations or zero-coupon corporate bonds or annuities that guarantee rates for five years. Zero-coupon instruments require the investor to pay only a small percentage of the face value. At 11.20 percent, the current rate, money doubles in 6.6 years.

Investors who are middle-aged or younger should look for a growth-oriented mutual fund, Keller says. But he also says it is wise to check the fund's investment philosphy and watch out for funds that have grown very rapidly or changed managers frequently.