They gather in clusters in the marble halls outside the committee room, sometimes two or more of them to a politician, sometimes one on one. Inside, they watch intently as the debate meanders along the parliamentarian trial, confident that their very presence has an effect on the legislators.

For Washington's high-powered, influential banking lobbyists, the action these days is at the Rayburn House Office Building, where members of the Banking, Currency and Urban Affairs Committee are debating on omnibus bank reform bill. Not so long ago, many of these lobbyists were predicting to their clients around the country that the bill probably would die in subcommittee. But thanks mainly to the revelations about former budger director Bert Lance's bank dealings - and the public's perception that Lance's was not an isolated case - some sort of reform legislations most likely will be voted by Congress during this season.

The lobbyists - most of them now resigned to the prospect of legislation - are hard to work trying to fashion the measure into something their clients can live with.

"What we are seeking is legislation that gives bank regulators a scalpel rather than a sledgehammer," says Gerald Lowrie, the chief lobbyist for the American Bankers Association. The ABA and other banking groups are backing the far milder Senate version of the legislation, which passed last August before details of the Lance affair spurred the need for tougher legislation.

With a membership of 14,000 representing 93 percent of the nation's banks, the ABA is among the richest and most persuasive lobbying outfits around this town. According to congressional staffers, the ABA has refined its lobbying techniques in recent years so that now its Washington office can trigger a national outpouring by members by the push of of a computer button.

The ABA's "contact bankers" - select, politically savvy members of the association who also have clout in their communities - are strategically located and can be sent into action at a moment's notice. The activities of state and national governments are cearefully monitored, and politicians are quick to learn if the ABA hears of any threatening legislation in the works.

"Most of the members (of Congress) don't realize the reason that they are hearing from bankers back in their district is that Mr. Lawry over on Connecticut Avenue has pressed the computer button," says one staff member in grudging admiration for the ABA's well-oiled operation.

But back in the mid 1960s, the ABA's lobbying operation was considered inadequate by some of the bigger banks. So they hired their own lobbyists, and today some of these institutions have whole teams at work. For example, First National Bank of Boston has three registered lobbyists, and Bank of America and First National Bank of Chicago have two each. Other banking Goliaths with their own registered lobbyists here are Chase Manhattan, Security Pacific, Chemical, Irving Trust, and Citibank.

Many of the top lobbyists are former top aides of the Senate Banking Committee, which of course is a key target of their lobbying. They include James Cash, former professional staff member of the committee, now with the ABA; John Yingling, a former chief clerk of the committee, now with the Citibank; Donald Rogers, former assistant counsel to the committee, now representing the Association of Registered Banking Holding Cos; and Matthew Hale, former general counsel, who now works for a law firm in Washington that represents banking interests.

Most the country's rural and suburban bankers belong to the Independent Bankers Association of America, which represents some 7,300 banks, most with deposits of less than $25 million. At times, the IBAA and the ABA squabble, and the members of the smaller association who also belong to the bigger one threaten revolution. But according to observers, the two organizations seem to have hammered out a united front in lobbying on the current bank reform legislation.

Last summer, after the Bert Lance affair broke, the ABA seemed unsure of what public posture to take. After all, Lance had been on the ABA's governing council and he had been looked upon as banking friend in the administration. On Sept. 12, ABA President-elect A. A. Milligan set the tone for the membership - and put a little distance between the association and Lance - by declaring in a speech:

"Quite frankly, I see red when I hear anyone dismiss these overdrafts and improper disclosures about loans as being "just typical business practices among bankers'."

In the months since then, the flow of letters to congressmen in opposition to the House bill has repeated this theme, which had been disseminated to the ABA members.

Last Tuesday, on the first day of full committee debate, members voted to change the bill's name from "The Safe Banking Act," a designation that nettled bankers with its suggestion that banking as currently practiced is unsafe. A minor irony is that the amendment to change the name to the Financial Institutions Reform Act was introduced by freshman Rep. D. Douglas Barnard (D-Ga.). Before coming to Washington, Barnard was a board member of Georgia Railroad Bank and Trust Co. in Augusta, the same institution that made generous loans to Bert Lance.

To ABA lobbyist Lowrie, the name change "was a signal that the committee was willing to legislate on substance."

Indeed, not long after winning that minor victory, the bank lobbyists teamed with lobbyists from the second biggest repository of assets in the U.S., the insurance industry, for a major win. Under the Clayton Act, competing corporations may not have representatives on each others' boards of directors. But a loophole in the Clayton Act specifically excludes interlocks involvingbank and nonbank boards. As a result, the country's biggest banks and insurance companies exchange board members, even though the two financial institutions may compete with each other for, among other things, real estate financing business.

A section of the bill would have closed this loophole, causing the Clayton Act to apply to banks in the same way it applies to other business. According to Lowrie, the ABA, major banks, insurance companies and insurance trade associations met at the ABA headquarters here to plan a unified attack on this provision of the bill. During subcommittee hearings on the measure, Rep. Garry Brown (R-Mich.), who has a reputation of being close to banking interests, had the section closing the loophole in the Clayton Act deleted from the bill. An attempt by Rep. Fernand St. Germain (D.R.I.), the bill's author, to reinstate the section in committee was defeated 23 to 16. St Germain plans to try again to get the section reinstated when the legislation reaches the floor of the House.

The bankers lost on one measure last week. A committee member tried to get the country's 8,700 state banks excluded from a section of the bill that sets a lending limit to bank insiders of 10 percent of the bank's capital account. Currently each state sets the limits, which can go as high as 25 percent. Moreover, bankers can borrow 25 percent for themselves, 25 percent for their companies and 25 percent for their political campaigns, among other things. The house bill allows a banker to borrow an aggregate of 10 percent.

ABA's Lowrie says his organization will try to get the amendment through when the bill reaches the floor. He said he will be in touch with the lobbyist for the Conference of State Superintendents of Banks to see if that group wants to team up with the ABA on the issue.

The lobbyist hopes a section of the bill that sets a limit on the growth of bank holding companies will be defeated tomorrow. Another controversial section of the bill would limit access by investigators to an individual's bank records. A bizarre coalition of lobbyists from the ABA and the American Civil Liberties Union seeks passage of this section of the bill. The Justice Department and the Securities and Exchange Commission, among other government investigative agencies, worry that such a law would make their job impossible.