Five years ago, 73 percent of the budget of the Securities and Exchange Commission came from fees charged corporations and broker-dealers.

Last year, the SEC collected about $26.5 million in fees, which amounted to 43 percent of the commission's $62 million budget.

Last week, SEC Chairman Harold M. Williams announced a formal study of the agency's fee structure.

However, the commission's comptroller has began reviewing fees for some months at the behest of some members of Congress. They voiced concern about the declining contribution of fees to the agency's growing budget.

Williams, in his announcement, makes it clear the commission is looking for new ways to offset the taxpayer's contribution to the agency's finances.

Among the areas under study, according to the announcement, is "the relationship between the size of the fees and the expense incurred by the commission in rendering... services."

Most of the fees now come from companies registering new stock offerings and from stock trades.

The commission charges a company 20 cents for every $1,000 in new shares that it is registering.

On stock trades, it collects 3 1/3 cents on every $1,000 worth of stock traded on all exchanges and on the over-the-counter market.

In fiscal 1978, the commission collected $14.5 million from fees charged for registration statements and $7.2 million from stock trades.

Another $4.2 million in fees was collected by the SEC for processing other corporate filings, such as proxy statements and annual reports.

According to an SEC spokesman during one year in the mid-1960s, when there were record numbers of new stock offerings and feverish trading activity on the exchanges the SEC actually collected more in fees than it spent.

But the commission's budget does not rise or fall with its collection of fees. "Every dime we collect goes to the Treasury. Then we get our budget from the Office of Management and Budget," said the spokesman.