Evidence of the United States' economic rebound surfaced in greater detail last week, and the stock market headed sharply lower late in the week.

What's going on here? Can't investors find joy in the so-called good economic news?

Theories about these events are as numerous as Washington newsletters. For one thing, continued high interest rates and economic data below the surface of recent government reports indicate that inflation has not been slowed down. Leading area banks are expected to post 14 percent prime interest rates this morning and local mortgage rates already are at or above that level, bringing housing sales here to a halt.

But there also is a broad consensus that national and local economic developments alone do not sway investors much any more. More and more Washingtonians with money to invest are looking overseas at the same time foreigners are investing some of their money in this region. Both groups are taking similar actions to diversify the sources of potential wealth. g

For example, Allied Capital Corp., a Washington financial holding company and small business investing firm, reached tentative agreement last week to sell 250,000 shares for $2.5 million to a subsidiary of Enterprises Quilmes S.A., of Luxembourg.

One local economist, David Ernst of Evans Economics Inc., noted that even as the U.S. economy is moving out of recession, a European slowdown has been confirmed. France and West Germany suffered declining output in the second quarter while Great Britian's economy has remained weak. Italy's economy started on a downward spiral in May, added Ernst, director of international economics for Evans.

He found that conditions in Japan are better than in Europe and predicted that, overall, there will be no prolonged reduction in worldwide economic activity. If the Iran-Iraq war ends within a few months, the moderate European recession should be over by early 1981, he added.

But, if the war drags on for six months or more, "this would result in an increase in the price of oil to roughly $50 per barrel and could turn the mild, unsynchronbized world downturn into a severe world recession like 1974-1975," Ernst concluded.

Faced with such uncertainties beyond U.S. shores, some investors are looking further than the volatile world of stocks, bonds and commodities to a relatively new mutual fund based in Baltimore that invests in business enterprises and government bonds around the globe. This spreads risk throughout many national economics and has the potential for taking advantage of an upward business cycle in one region at a time of recession elsewhere.

There has been a significant increase in interest in such international investments by large and sophisticated investors in recent years. Now, the Baltimore fund, Rowe Price International Fund Inc., is getting ready sometime in the next six months to offer shares to average investors by reducing the current minimum initial investment of $25,000 to $5,000.

Rowe Price International Fund had no operations prior to May 9, but assets expanded to $12 million by the end of June, now exceed $30 million and are expected to top $100 million by the end of the year. The fund is managed by a young joint venture of Rowe Price Associates Inc., the big Baltimore investment counseling firm, and Robert Fleming Holdings Ltd., a London merchant bank and investment management organization.

Through its affiliated companies, Fleming Holdings has offices in Zurich, Tokyo, Hong Kong and Singapore and is the major foreign investor in Japan and Southeast Asia.

The British concern is thus attaching its worldwide investment experience to the U.S. investment couseling and marketing skills of Rowe Price, the largest manager of money in this region, with $5 billion in private accounts and $4 billion in seven no-load (no sales commission) mutual funds under its wings.

One indication of growing interest in international investing is a seminar scheduled on Wednesday in New York by Rowe Price-Fleming International. It will focus on the Pacific Basin through analysis of prospects for Japan, Hong Kong, Singapore, Malaysia and Australia.

Rowe Price International Fund's stock investments are heavily weighted toward Far Eastern markets, "where we expect the thrust of long-term growth and near-term economic momentum to be strongest," said officers of the fund in a report to stockholders in mid-July. As of June 30, more than 25 percent of the market value of the fund's holdings were invested in Japanese stocks and about 15 percent were in electronics.

"The Japanese stock markets are the largest and most diverse outside of the United States and offer a broad range of interesting individual investment opportunities," the fund managers stated.

Stock investments in Japan, as of June 30, included such companies as Fuji Photo Film, Honda Motor Co., Mitsubishi Corp. and Pioneer Electronic. In other countries, investments included stock of Deutsche Bank and Siemens of West Germany Royal Dutch Petroleum in Holland Broken Hill Proprietary, Australia's largest corporation with energy, mining and steel interests and Yeo Hiap Seng of Singapore, which owns the Pepsi Cola franchise for Malaysia.

Government bonds included those of Holland, Australia, Denmark, New Zealand and Japan.

It is not possible to measure the gain for investors from the new fund, because of its short history. But net asset value per share rose 4.5 percent from May 9 to June 30, despite the cost of establishing initial portfolio positions.

The chief economist for T. Rowe Price Associates, meanwhile, has offered an economic forecast of the sort that calls for broad investing to protect against risks.Despite the recent indicators of economic stength in the United States, the recession has not run its course and higher umemployment is likely, said Ben E. Laden last week.

There is but an apparent economic turnaround caused by the temporary boost that resulted when credit controls (imposed in March) were lifted over the summer, according to his assessment. "The experience with credit controls has distorted the normal cyclical relationships and is now giving misleading signals of strength to the economy. . . . We conclude that the pieces are not yet in place for a strong, sustainable recovery," Laden stated.

Under this scenario, credit controls first caused a much steeper slide than otherwise would have occurred. When controls were lifted, demand for credit from consumers and business expanded, the supply of money grew rapidly and interest rates started back toward peak levels.

Behind the rosy statistics of recent weeks, Laden finds a number of factors that spell out continutation of the economic slump: further inventory reduction by business, which restrains new hiring high interest rates to stifle housing and auto sales sluggish consumer spending because of continuing high inflation and rising taxes another 6-to-12 months of weakness in spending by business for new plants and equipment and the developing overseas recession, which will dampen U.S. export sales.