Congressional mail carriers will be groaning in coming weeks if the nation's largest financial trade associations succeed in an ambitious grass-roots lobbying effort to repeal the 10 percent withholding tax on interest and dividends before it goes into effect July 1.

The American Bankers Association (ABA) already has received requests from 9,000 of its 13,000 member banks for kits that contain sample speeches--including special versions for senior citizens and areas of high unemployment--letters to the editor and statements urging customers to write their congressmen to kill the new requirement. An ABA spokesman said that nearly 14 million flyers that can be stuffed in customer account statements also have been ordered.

Similar campaigns are being run by groups representing savings and loans, savings banks and credit unions. Bruce Jolly, Washington counsel for the Credit Union National Association, which represents 20,000 credit unions and 47 million customers, said, "No one knows what kind of public opinion engine we've turned on. With us, the banks and the savings and loans we can reach virtually every citizen in America."

Some members of Congress already have received thousands of letters and postcards attacking the requirement, and institutions are just sending out millions of flyers in customers' year-end statements. Thursday, Rep. Norman E. D'Amours (D-N.H.) introduced a repeal bill with 60 co-sponsors.

The financial lobbyists acknowledge that despite the unprecedented effort their repeal fight will be difficult because of record federal deficits. The new tax provision is expected eventually to add about $3 billion a year to federal tax receipts.

The bankers fought the new provision unsuccessfully last summer, when it was passed as part of the tax bill. An amendment to delete withholding was defeated, 50 to 47, in the Senate.

The bill had strong support last summer from the Internal Revenue Service and such congressional sponsors as Sen. Robert J. Dole (R-Kan.), chairman of the Finance Committee. They argue that this is just collecting money that is already owed on the $300 billion in interest and dividends paid out each year. They also say the new rule is no more onerous than the withholding of wages.

Some large banks and other trade groups representing the securities industry, money market funds and the Chamber of Commerce have not joined the campaign, either because they have other legislative priorities or consider the fight hopeless.

John Maloney, a spokesman for Citibank, which has more than a million customers in the New York area, said his bank is not participating in the repeal drive. "We're not against it. We're just not doing a mailing," he said.

Riggs National Bank, Washington's largest, is still studying the issue, an official said. Maryland National Bank, the region's largest, is an active participant in the campaign, according to the ABA.

Virginia National Bank spokesman Joe Ward in Richmond said his bank favored repeal, but he didn't think its marketing directors had started lobbying customers for help.

At least one area bank has already started sending "statement stuffers" to customers with routine mailings of other material.

Dan Buser, an ABA spokesman, said his group supports cutting the federal deficits, like a group of business and financial leaders planning their own publicity campaign. But the ABA doesn't find its repeal effort inconsistent with attempts to slash the deficits.

"We think the federal deficit needs to be controlled," he said. "We just strongly feel that withholding on interest and dividends doesn't contribute to that and isn't an answer." The bankers support other increased compliance efforts, such as new reporting requirements, he said.

In its publicity kits, the ABA estimates that withholding will cost consumers at least $1.5 billion in lost earnings on some $30 billion in interest and dividend income that will be withheld from accounts and turned over to the Treasury.

There are no public estimates on how much profit the industry will lose by not being able to lend out that $30 billion, much of which lies dormant in customer accounts.

The ABA estimates the industry will have to spend $1.5 billion in staff training and computer time to implement the new procedures.

William H. Kennedy Jr., the ABA president, outlined the campaign in a Nov. 5 letter to the group's members. "This tax law was imposed for political reasons and it will have to be repealed politically," he wrote. America's banking customers must be educated about what withholding means to them personally, he added, "and then we must mobilize them to set up a clamor for repeal."

Involving the customers will get the message to Congress that there is a mandate for repeal, the ABA material states. "And, if Congress fails to act, your customers will blame the Congress, not the banks," it added, referring to an objective of the campaign that some bankers say may be as important as the repeal goal.

Ohio bankers already have been stirring up their customers. Rep. Michael Oxley (R-Ohio), for instance, has been busy the past month answering the 5,000 letters and postcards urging repeal.

Rep. Marcy Kaptur, a newly elected Democrat from Toledo and a new member of the House Banking Commmittee, will be getting 5,000 signed repeal cards from customers of the Sylvania Savings Bank by certified mail next week, Sylvania marketing director Walter Coe said yesterday.

T. Herbert Stevenson, vice president of the Western Ohio National Bank and Trust Co. of Covington, near Dayton, said he collected 2,700 signatures opposing the tax in a 2 1/2-day campaign last summer. His consortium of a dozen local area financial institutions already say it has 1,000 repeal notices signed and waiting for Rep. Thomas N. Kindness (R-Ohio), he said.

ABA spokesman Fritz Elmendorf said that IRS Commissioner Roscoe Egger Jr. told a group of banking executives recently that he believed the lobbying campaign would behave like a rock tossed in a pond: create a big splash, then some ripples that would die away. He said Egger will be right "if this is not a major public issue by February."

But he also compared the political clout of his members to that of the National Rifle Association. "They can generate hundreds of letters per congressional district," he said. "We're talking about tens of thousands" per district.