Q. My wife and I are both retirees and have been holding 50 shares of UAL Inc. for some time. Do you think we should sell this stock?

A. While the industry skies aren't friendly right now, this stock should provide longer-term happiness.Hold your shares of UAL Inc. (around $107 a share, New York Stock Exchange), the holding company for United Airlines, because, no matter what happens with the economy, it will remain a global carrier with an excellent reputation, said Julius Maldutis, analyst with Salomon Brothers.

Despite the fact United's passenger traffic has risen 9 percent this year, its stock doesn't merit a rave review because of the many industrywide concerns.

"Most airlines will issue poor year-end reports in late January or early February, and the UAL stock price is not fully discounted to reflect this," said Maldutis. "There is uncertainty among the airlines regarding their cash flow because of rising fuel costs."

Q. What are your thoughts on W.R. Grace Co.? Is it a good stock buy?

A. This stock should keep your broker in your good graces.

Buy shares of W.R. Grace Co. (around $25, NYSE), the chemical, energy and consumer product firm, because of their 7 percent yield, reasonable price and lack of downside risk, said Stuart Pulvirent, analyst with Shearson Lehman Brothers.

"Grace has been trimming its fat and this should offset some risks of the economic environment," said Pulvirent. "Another plus is that management has focused its attention and research efforts on specialty chemicals, rather than all types of chemicals."

Q. My brother and I inherited 500 shares of May Department Stores from my aunt, who worked there for many years. We want to keep them for sentimental purposes, but, with retailing being slow, should we sell?

A. Don't keep any stock simply for sentimental purposes. Its role is that of an investment, not a keepsake.

However, since this is a bad time to be selling any downtrodden retailing stock, you would do well to hold on to those shares of May Department Stores Co. (around $44, NYSE), the operator of department, discount and shoe stores. The retailing industry has been under pressure because of the slow economy, and this situation is expected to continue in 1991.

"The last few months haven't been generous to May, and its early Christmas figures were off by 5 percent," explained Wayne Hood, analyst with Prudential-Bache Securities, who believes you should ride out the present economic storm.

Q. Our financial adviser has been pushing H&R Block Inc. as a hidden gem. What do you think of this stock?

A. Read my lips: Taxes are a booming business.

Buy shares of H&R Block Inc. (around $44, NYSE), the tax return preparation, database and personal services firm, based on their long-term potential, said Judy Scott, analyst with Robert W. Baird & Co.

There will be positive fallout for Block from tax changes, and its electronic filing system is expected to again boost profits as it did last year. Other pluses are the fact that the firm has automated its bookkeeping and increased its highly profitable executive tax service to 300 offices nationwide.

"As it becomes more aggressive with this service, I am positive that this will strongly improve Block's profits," said Scott.