These are dangerous times for investors. Not because of what may happen to interest rates, inflation, the dollar or even the Dow Jones industrial average. No, this is a dangerous time because the Temptation Index is at an all-time high.

Everywhere an investor looks there are stocks that simply cry out to be bought. Temptation is everywhere. Bank stocks, thrift stocks, real estate and retail stocks, even some high-technology stocks are so cheap that investors can barely restrain themselves from calling their brokers and hollering "Buy."

But when is cheap cheap? And when is cheap not only dear, but dangerous?

Those are the questions that are on the minds of many Washington area investors these days.

Take a look at Perpetual Savings Bank, selling at $3.13, a stock that once sold for $19.25. True, that was in the days before the real estate market soured, requiring $50 million loan reserves. But even so, the temptation to acquire some of those shares must be great.

Suppose Perpetual rides it out, goes one side of the argument. If the stock recovers, it could be a big winner. Oh, sure, goes the other side of the argument. Unless you know what is really going on inside the thrifts and banks, and unless you know what the regulators are up to, you'd better keep your money in Treasury bills.

And what of Kay Jewelers Inc.? It was a real sparkler at $24.38 not long ago. Now it is selling at $7.50. Rumors of buyouts and mergers abound but sales are soft and the short sellers are circling in force. Will the stock recover? And when?

How about Insituform East Inc.? The stock, at $4, is so low that the company has begun to buy back its own shares. Remember when it sold for $27.50 a share? Of course, there are a few problems, including a skid in the company's earning to 6 cents a share in the most recent quarter from 8 cents a year earlier. The company, which repairs sewer pipes without digging them up, says it is installing more feet of pipe than ever before but the pipe is of smaller diameter and thus the work is providing the firm with less profit.

And then there's NVR L.P., the home building firm. Its stock is down to $2.75 from a lofty $21.75 in the good old days. Now, do you happen to know when the real estate market is going to pick up?

Finally, there's the Rouse Co. It was a big player in the development of Harborplace in Baltimore, the South Street Seaport in New York and Faneuil Hall in Boston. Here, too, the short sellers are all over the stock, which annoys analyst Robert A. Frank of Alex. Brown & Sons. He says it is mindless to short the stock just because Rouse is in the real estate and development business and because that business is out of favor. Frank says the stock, at $23.13, is a strong buy. Its five-year high was $29.25.

And so it goes. Rarely have the prices of so many stocks been so low and so tempting to investors. But rarely, too, has the price of being wrong been quite so high.

So much for grand plans. The plan of JHM Mortgage Securities L.P. of McLean to buy the mortgage-related securities or the mortgage-payment servicing operations of troubled thrift institutions is temporarily on hold.

As reported in this column last week, JHM received a letter on March 21 from the Office of Thrift Supervision, which regulates savings and loans.

The OTS letter told JHM that thrift regulations affecting limited partnerships would permit federal savings associations to invest in JHM shares, called preferred units. The units trade on the New York Stock Exchange.

The letter was important, JHM officials said, because it would allow JHM to use its shares to buy investments or mortgage service operations from thrifts that were being forced to sell, and probably would sell at relatively low prices.

"In crisis there is opportunity," said Chairman Stephen P. Gavula.

Well, maybe not.

The day after the column appeared, JHM officials received another letter from the OTS, this one from the new chief counsel, Harris Weinstein.

According to JHM officials, the letter from Weinstein said the agency had "determined that the issues covered by its March 21, 1990, letter {to JHM} merit further study." Until the agency finishes its review, Weinstein added, "federal savings associations may not rely on the contents of the March 21 letter."

Needless to say, JHM officials were somewhat disconcerted to get one letter from the OTS that said "go" and a second letter that said, "stop."

JHM quickly requested a meeting with the agency to review the matter. Gavula noted, "We spent seven months prior to the OTS's March 21 letter, carefully reviewing with the OTS staff our company's operations and program to bring liquidity to the thrift market.

"We are confident that when the OTS new chief counsel studies our program and the benefits that we can provide to savings associations, under the new capital rules, that the OTS will reconfirm its prior position."

The next day, however, the OTS announced flatly that it had withdrawn its first letter, "pending further study." The agency didn't say when that study might be completed.

Richard Fontaine, who once managed the T. Rowe Price Capital Appreciation Fund, now runs his own money management company in Baltimore. In addition to managing private money, Fontaine has opened up a new public no-load mutual fund called, quite naturally, the Fontaine Capital Appreciation Fund.

The charter of the fund gives Fontaine a wide range of investment choices, including going to 100 percent cash and investing as much as 10 percent of his money in foreign stocks or options and stock index futures.

Usually, however, Fontaine says, he will keep most of his money in stocks that are undervalued or that look like they will benefit from a reorganization, acquisition or merger.

From the first six months of the fund's operation, from Sept. 30 through March 31, the fund rose 4.8 percent compared with a 2.3 percent gain for the Dow Jones industrial average and a drop of 1.1 percent for the Standard & Poor's 500.

In 1989, Microlog Corp. of Germantown, Md., formerly Old Dominion Systems, saw its shares rise 256 percent, making it the year's top gainer among area stocks. Microlog, which is in the business of developing voice-message systems, also saw its profits triple during that year. But after a fairly good first quarter, it reported a second-quarter loss of $381,000, breaking the upward trend.

The firm also sold another 1 million shares, diluting the earnings per share.

So the market, which shows little sympathy for any company that stumbles, has marked Microlog's shares down from $9.50 at the beginning of the year to $5.75, a loss of 39.4 percent. However, the shares were as low as $4 on April 30.

One of the problems, said Chairman J.G. Hartwell, was that Microlog expanded its marketing force and many of the sales people were new to their jobs. "It took longer than anticipated to raise the effectiveness of our new salespersons to desired levels," said Hartwell.

Avemco Inc., the aviation insurer with headquarters in Frederick, Md., has authorized the buyback of another 1 million of its shares. The firm, said Chairman William P. Condon, already has bought back 1.9 million shares. If and when the new buyback is completed, for a total of 3 million shares, the company will have taken back about one-third of its stock over a period of several years.

At the moment, Condon said, the buybacks appear to be the best use of the company's excess capital. Generally, said Condon, the company tries to buy large blocks of stock when they are offered to the company. One of the benefits of a buyback is that it reduces the number of shares outstanding, and thus improves the company's earnings per share. That, in itself, is often enough to help a lagging stock.

Avemco has been faced with a down cycle in its business -- which Condon calls "the toughest three years I've seen." But there are signs that business is turning up. Avemco at $24.88 is not far off its five-year high of $28.75.endquad