It was a great first quarter of 1991 for investors in the stock market, the best in four years.

The Dow Jones average of 30 industrials closed out the quarter Thursday with a 3.71 point decline to 2,913.86 for the day but a 280.20 point gain for the quarter, its largest quarterly increase since the first three months of 1987 when the Dow surged 408.74 points.Thursday marked the end of first-quarter trading because markets were closed Friday for the Good Friday holiday.

Will the second quarter of 1991 bring investors more such profits? If "soaring optimism" by Americans in general and investors in particular is a good bellwether, it ought to.

According to the March survey of U.S. investors conducted by Fidelity Investments, which has a major investment center in Salt Lake City, its "investor sentiment index" soared from 73.1 in February to 88.1 for this month, the largest monthly increase ever.

According to Michael Hines, Fidelity's vice president of Marketing, another index, the "index of investor expectations," which measures what investors expect business conditions and their own financial situations will be in the future, rose from 62.9 in February to 83.7 for March - the highest since last year at this time.

Trouble is, investor sentiment can fluctuate as quickly as the financial markets, said Hines.

"While investors are more optimistic now than they've been since August, it's likely that they will vacillate between periods of optimism and pessimism over the coming months as they respond to conflicting economic data," he said.

Does that mean the current optimism - generated by the quick and successful conclusion to the Persian Gulf war - is an illusion? No, said Hines, the confidence is real, "but it will take some time for the confidence to convert to purchases." Consumer spending is credited with some two-thirds of the power behind the national economy.

Despite the first-quarter gains in the stock market, most of which, surprisingly, took place when the outcome of the war was still very much in doubt, Hines said the soaring consumer optimism revealed this month has had only minor impact on the nation's mutual funds industry.

The survey showed that "net purchase intentions" of mutual fund investors for stock funds remained high this month at 28 percent but below February's 34 percent.

"Investors are digesting the changes they've seen in the stock market and world events over the past month," he said.

Still, the survey showed that 79 percent of all investors believe that now is a good time to buy a house, up from 59 percent last October, and 69 percent believe now is a good time to buy a car, up from 53 percent in October.

Despite all this bullish sentiment, Utah-based investment adviser Howard Ruff does not share the optimism. He believes the stock market that appears to be a bull may actually be a "bear trap."

While acknowledging that all of his charts and indicators confirm an upward trend in the market, Ruff is suspicious. In his March 25 newsletter "The Ruff Times," he says the market remains vulnerable for four reasons:

1. It is overvalued based on price-to-dividend, price-to-earnings, and price-to-book-value ratios, and yield.

2. The Dow momentum has broken down after only two weeks in bullish territory.

3. The number of stocks hitting new highs is contracting sharply even as the market flirts with all-time highs.

4. Bullish Sentiment is rampant, albeit "a bit dented" by a 62-point decline March 20.

"If you put a gun to my head and made me bet," said Ruff, "I would bet that the stock market's recent rally either is becoming, or will become, a gigantic bear trap."