What's so bad about feeling good? Hitting record highs on Wall Street has never been greeted by so many nervous and twitchy smiles as it has been in 1990. A rally based primarily on an easing of interest rates, normally cause for jubilation, has been deemed by many experts to be merely a pleasant surprise. They can't believe that any interest rate downturn will be pronounced enough to continue to boost the market long-term.

This admittedly spunky stock market is still trapped in a trading range, they reason, because the good news still won't be terrific and the bad news won't be traumatic. Even record-setting days don't dramatically alter such basic circumstances, but just make that trading range a bit broader."While I'd advise the investor to put money in equities because the economy should generate favorable earnings the next several quarters, I'd also tell him to prepare to be nimble," advised Joe McAlinden, director of research for Dillon Reed. "It's quite possible that by year-end the bull market may come to an end, and the next six months constitute the final climactic move."

Emotion should continue to play a role in this market.

"Because the pluses and negatives pretty much equal out this year, there will be tremendous focus on daily news events and economic figures," said Marshall Acuff Jr., portfolio strategist for Smith Barney, Harris Upham & Co., who believes the time to buy this year is on market downturns. "Just keep firmly in mind that this market isn't as forgiving as it has been in the past, and that this game requires being a stockpicker."

The "surest bets" for 1990 - according to Wall Street portfolio strategists interviewed for this column - include International Business Machines, Bristol-Myers Squibb and Motorola Inc. All three stocks were recommended by more than one of the four strategists interviewed, based on the logic that these stocks are oozing with earnings potential in both the United States and abroad.

"In general, don't look at this market as either friend or foe, for it will lurch along a bit this year, but should really do much better in coming years," said Steve Einhorn, chief portfolio strategist for Goldman Sachs. "The important market theme is the growth stock, as we experience subdued economic growth the next several years."

It's a market that's still trying to find its personality in the wake of the dramatic 1980s.

"The decade of debt is behind us and growth companies should be taking over," predicted Mary Farrell, portfolio strategist with PaineWebber Inc. "As a result, you should emphasize companies with foreign sales, particularly to Eastern Europe, and good `niche' stocks of companies that provide something unique."

Interest rates, of course, are a key factor and the news there is expected to be fairly good. While Acuff does acknowledge a likelihood of higher long-term interest rates by year-end, the other three strategists predict that rates will decline.

Here are the latest recommendations on the proper mix of investments for 1990, as well as the strongest stock picks:

McAlinden of Dillon Reed, bullish at least for the time being, has a model portfolio that's a whopping 95 percent in stocks, only 5 percent in cash and nothing in bonds. His favorite stock in technology is Motorola; in machinery, Foxboro Co.; in materials, Amax Inc.; and, in energy, Burlington Resources.

Acuff of Smith Barney sports a model portfolio that's a considerably more balanced 45 percent stocks, 35 percent bonds and 20 percent cash. Top selections are IBM, Bristol-Myers Squibb, Digital Equipment, Deere & Co. and Dillard Department Stores.

Einhorn of Goldman Sachs believes the ideal mix is 50 percent stocks, 30 percent bonds (mostly long-term government bonds) and 20 percent cash. His picks are Bristol-Myers Squibb, Merck & Co., Syntex Corp., Schlumberger Ltd., Dresser Industries, Kerr-McGee, Gap Inc., Wal-Mart Stores, Gillette Co., Compaq Computer and Ingersoll-Rand.

Farrell of PaineWebber says the typical investor should have a portfolio of 60 percent stocks, 30 percent bonds and 10 percent cash. Among companies with solid foreign sales, she likes the stock of IBM, Motorola, Minnesota Mining & Manufacturing, Coca-Cola Co. and Philip Morris Cos. In "niche" stocks, her preferences are the Allen Group, A.L. Labs and Vons Cos.