A small number of investors -- about 50 big banks, insurers and pension funds -- hold huge, potentially controlling blocks of voting stock in the nation's 38 biggest oil and energy conglomerates, according to a study released yesterday by Corporate Data Exchange.

The study also showed that within each of the 38 big energy firms -- which include all the big-name oil companies -- ownership is heavily concentrated. The top five investors on the average held one fifth of all the stock.

The study, funded by the United Presbyterian Church, United Methodist Church, Stern Fund and several other groups, shows the energy industry is concentrated in relatively few firms. It is not nearly as concentrated, however, as the U.S. auto industry which has only four major producers.

All told, according to CDE, the 142 biggest U.S. energy companies had $517 billion in revenue worldwide in 1978. (This includes non-energy revenues of some firms also engaged in the energy business. Some of the firms are known mainly for other products but have substantial mineral operations.)

But a handful dominated. Exxon alone had $64 billion; Mobil, $37 billion; Texaco, $29 billion; Standard of California, $20 billion; Gulf, $19.9 billion; Standard of Indiana, $16.4 billion; Atlantic Richfield, $12.7 billion and Shell, $11 billion. The top 10 had nearly half the $17 billion total.

Ownership and control was concentrated, too. Although the 38 biggest companies had 5,200,000 investors, the 50 institutional like J.P. Morgan & Co. (parent company of Morgan Guaranty Trust), Citicorp., Chase Manhattan, Lord Abbett and Co., the Du Pont family and the like held an averave of 15 percent of the voting stock in each of the 38 giants. Control of only a few percent of the voting stock in a company normally gives the holder a substantial policy voice if he chooses to use it.

J.P. Morgan, for example, through its trust department and other forms of holdings, held at least 1 percent of the voting stock in 14 of the 38 biggest energy companies. This included Exxon, Tenneco, El Paso Gas, Panhandle Eastern Pipeline, Mobil and several smaller companies. Prudential had more than 1-percent of the voting stock in the nine firms.

The big teacher pension fund, TIAA-CREF, was a big holder of stock in firms like Texaco, Texas Gas, Conoco, Shell, Panhandle, Gulf and many others.

Some individual banks and family interests hold enormous blocks of stock in major companies: Getty family interests had 58 percent of Getty Oil; Mellon family, 18 percent of Gulf; Keck family, 30 percent of Superior Oil; Pew family, 30 percent of Sun Oil; and some banks 5 to 10 percent of medium to big companies.

"It's a danger to a democratic society when a very limited number of investors have such a big say over such a significant industry -- it poses real problems for democratic decision-making," said Michael Locker, co-director of CDE's energy project in outlining his view of the study's findings.