Manufacturers Hanover Trust Co., the nation's fourth-largest bank, said yesterday that it had failed to report to the Treasury Department about $140 million in foreign currency transactions it had with foreign banks during the last 4 1/2 years.

Manufacturers Hanover, like many other banks, began to review its compliance with federal reporting requirements after the Bank of Boston, that city's biggest, was fined $500,000 last month for reporting violations. Early this month, Boston's other two big banks -- Bank of New England and Shawmut Bank -- said an audit turned up cash transactions they failed to report to the government, and on Tuesday, Chemical Bank of New York said it discovered $25.9 million in cash transactions it did not report.

Since 1972, in an attempt to make it more difficult for drug traders and other criminals to "launder" their cash through the banking system, regulators have required banks to report to the Internal Revenue Service whenever a domestic customer makes a cash withdrawal or deposit bigger than $10,000. In 1980, that requirement was expanded to include cash transactions with foreign commercial banks.

Manufacturers said yesterday that all the violations were concentrated in the department that accepts dollars collected by foreign banks and shipped to Manufacturers Hanover. A spokesman for the giant New York bank said it now has filed all 1,400 late reports and said auditors turned up no evidence of any money laundering in the transactions.

He said that all the transactions were "routine business" with about 40 foreign commercial banks in major tourist areas. Foreign banks regularly exchange local currencies for dollars carried by tourists and business travelers. After they accumulate enough dollars, they send them to their correspondent banks in the United States for deposit. U.S. banks similarly ship to correspondent banks abroad the pounds, francs and other currencies they exchange for dollars.

The Manufacturers Hanover spokesman said the 1,400 transactions with foreign banks represented about 1 percent of the roughly 120,000 reports the bank filed on time with the IRS. He said the 120,000 properly filed reports were on transactions made domestically. "I think the large number of reports filed on time shows that Manufacturers as an institution made an overall effort to comply with the law."

He said he could not explain why the bank's employes in charge of receiving dollar shipments from foreign banks did not file the required reports. He said they were aware that the reports were required. The spokesman said none of the employes -- whose names he did not know, he said -- had been fired, but he did not know whether any of them had been disciplined.

Bank of Boston was fined for $1.2 billion in cash transactions with three Swiss banks.

A spokesman for the Treasury Department said officials have not made a decision on how to proceed in either the Chemical Bank or Manufacturers Hanover cases.