With evidence mounting that some south Florida bankers have become unquestioning participants in that area's thriving illegal drug trade, the Treasury cracked down yesterday on requirements for reporting large currency transactions.

The new rules, which becomed effective in 30 days, would amend the Bank Secrecy Act of 1970 to require banks to report almost all deposits of cash of more than $10,000.

Among deposits exempted from the new reporting rules are those by established bank customers who also are American citizens and who operate large-cash-flow business such as retail outlets, bars, sports enterprises, rach tracks and amusement parks.

Currently, any depositor who a banker considers an established customer is exempted from the reporting requirement.

But Treasury officials suspect that some Florida bankers -- especially those in the Miami area -- count traffikers in Columbia drugs as their regular customers.

To support their suspicions, federal officials point to statistics.

The Federal Reserve Board, which tracks the currency flow among U.S. banks, reports that banks in south Florida are literally awash in cash.

The currency surplus in south Florida banks grew from $2.4 billion in 1978 to $3.9 billion in 1979, and Treasury officials has predicted it will top $6 billion this year.

In contrast to south Florida, where the Federal Reserve withdrew $4.2 billion in surplus currency in 1979, most of the other Fed areas in the country have a shortage of currency.

The Senate Banking Committee has scheduled hearings Thursday and Friday on banks and the narcotics money flow in south Florida. Bankers, regulators and law enforcement officials are among those scheduled to testify.

A committee staff investigator claims that it isn't unusual for relatively small banks in south Florida regularly to get deposits in cash of $1 million or more.

And according to some figures, drug traffic has outstripped tourism as south Florida's leading industry.

But for all the big dollars involved, there has been very little criminal prosecution against those allegedly involved in the drug-banking connection.

In 1977, a joint effort by the Drug Enforcement Administration and the FBI, called Operation Banco, was launched to trace the flow of drug funds.

However, the Miami Herald reported recenly that "Operation Banco has cost more than $1 million and produced only one major case."

The last big drug-related bank case involved Chemical Bank of New York. In that 1977 case, the authorities charged 445 illegal transactions a mounting to $8.5 million.

But a Treausry official says that the suspected bank transactions in south Florida make the Chemical case look like small change. "Hell, in Miami they do $8.5 million in a single bank transaction," he says.

The Treasury official expects that the newly tightened reporting rules will help regulators trace drug cash from banks outiside the country.

In the past, when banks off-shore transferred funds to U.S. banks, those deposits weren't reported to the Treasury. Under the new rules, when those deposits exceed $10,000, they must be reported.

"Now, when money comes into this country, we don't know it. But with the new controls, we will," the official said.