Retail stock brokers, feeling the pinch of last October's historic Wall Street slide, earned about 27 percent less from November to April, the Securities Industry Association reports.

A survey of securities brokers also showed that annual earnings for 1987 were down 3 percent from the same period the year before, said Edward O'Brien, the association's president.The survey, which covered 46,000 brokers, showed the average annual earnings of retail borkers declined to $93,959 from a record $97,100 the year before, O'Brien said.

Since the market's October fall, earnings for retail brokers have fallen to an annualized rate of $66,197, the association's survey said.

The trade organization, which represents 575 brokerages and investment banking companies, said volume on the New York Stock Exchanged averaged 1189.2 million shares for 1987 but declined 7.3 percent to 175.4 million shares one year later.

Earnings for institutional brokers also fell about 18 percent since the October market debacle.

But for all of 1987, brokers handling institutional investors reported a 3 percent increase in earnings.

Average earnings for institutional brokers increased during the year to $233,637 from $227,412.

Since October, earnings of institutional investors have declined to an annualized $191,071, the association said.