Like so many of the other pleaders who charge up Capitol Hill, the Special Committee for U.S. Exports was armed to the teeth.

The weapon that David C. Garfield carried in his briefcase as he walked across the gold carpet of the House Ways and Means Committee hearing room weighed 19 ounces.

In the armory of persuasion, that is heavy artillery. It was a position statement, carefully drawn, laden with statistics, large by any standard of congressional testimony, intended to tell his story and make his case.

Garfield heads that Special Committee for U.S. Exports, a group of businesses working furiously againist one of President Carter's leading tax "reform" proposals.

They are fighting Carter's recommendation that Congress end a tax provision that gives American exporting companies a subsidy of about $1 billion a year -- that is, taxes they don't have to pay. It is known as DISC, an acronym for a domestic international sales corporation.

The subsidy -- actually, a deferral of a portion of income tax on their export profits -- was granted to companies in 1971 as an incentive to sell more American products overseas and to stem the flow of dollars abroad.

So Garfield came down from New Jersey, where he is vice chairman of the Ingersoll Rand Co., with his 19-ounce statement, to tell Congress why business must -- absolutely must -- retain its billion-dollar break.

But no one gets to read a statement of that length to Ways and Means. There just isn't time, because the committee will have heard several hundred witnesses on tax reform before it begins drafting a final measure sometime in April.

Garfield was allowed a few minutes to summarize his statement. For all his trouble, he got only one question from the committee. Chairman Al Ullman (D-Ore.) thanked him for his testimony and Garfield's role as witness ended.

In the hearing room that day were some interested listeners who will play a role in the outcome of the DISC dispute on Capitol Hill.

Sitting near the front were William M. (Bill) Lee, an economist who shepherds the special-committee's interests here as an employe of one of Washington's major law firms, and Joseph E. Karth, a private consulant who used to be a Democratic congressman from Minnesota, member of Ways and Means, and friend of DISC.

Watching from the rear, a sort of lone eagle among all the corporate pinstripe suits, was Bill Pietz, an attorney for Public-interest definder of Carter's plan to end DISC.

Garfield's friends crowded around afterward. "It was pretty much what I expected," he said. "But i think people around the committee are beginning to see that the floating exchange rate is not a panacea."

If allusions to exchange rates and weighty statements and DISCS turn you off, don't despair. It is about power and money and the flexing of a lot of muscle around Congress.

A casual observer, watching Garfield that day a couple of weeks ago, might have concluded quickly that the Special Committee for U.S. Exports had fallen on its face in that effort to persuade congressional tax writers.

Not so. Actually, Garfield's appearance that day was a small and relatively insignificant part of a lobbying drive that has gone on almost continuously since 1975, when the special committee was formed to combat congressional attempts to kill DISC.

Back then, the special committee was successful to a degree. With help from then-Rep. Karth, who devised a formula that saved DISC but scaled down some of its benefits, the companies were able to maintain their expected sales tax break.

But then candidate Carter talked about ending the subsidy, the companies knew trouble lay ahead. Beginning last year, the special committee and its 1,200 members launched a campaign to dissuade the new president.

Their efforts have been largely unsuccessful, a development that now makes Congress -- specifically, the Ways and Means Committee -- the new pressure point.

For months, the DISC advocates have been rapping at the White House door, trying to get inside with their message for the president. They make telephone calls, they write letters, they seek appointments.

Mostly what they get in return are inconsequential meetings with middle-level functionaries, form-letter responury Department's middle-level offices and no sympathy.

Thomas O. Horst, one of the Treascials who answers part of the mail, describes the situation this way:

"We have a boilerplate letter that summarizes our position. I don't write a new response to every letter that comes in. I said when they send me a new letter. I'll respond differently . . . Most people think the DISC program is hokey -- you have to use imaginative economics to show any benefits from it."

Imaginations, of course, are stirred by the weight of the billion-dollar-a-year break the exporters would lose if President Carter has his way on tax reform.

But if other admistrations have been more open to the overtures of hard-pressed corporations, there is no sign that Big Business has been able to get a first base on this one at the White House.

As recently as last month, Carter denounced the DISC provision as an "unnecessary" and "unwarranted" subsidy. He called it "a giveaway to a few of the largest multinational corporations."

It is precisely that attitude toward the DISC that the special committee has tried, without success, to overcome inside the administration.

As Bill Lee recounts it, the committee tried everything. Efforts to meet with Treasurey Secretary W. Michael Blumethal and the late Laurence Woodworth, an assistant secretary before his death, failed. Meetings were arranged with lower-level officials, among them Tom Horst, who deals with international tax matters.

Special-committee delegates talked also with officials at the Departments of Agriculture and Commerce during the summer, when the administration was still working out "tax-reform" details, and they met with Robert S. Strauss, the president's special trade representative.

When the tax-policy issue moved into the White House by summer's end, efforts to meet with Stuart Elizenstat, the president's chief domestic advisor, were turned back, Lee reported.

"We just had difficulty getting through to anyone," he said. "We faced the same problem that some members of Congress have -- they can't get through."

And then as the White House took over final planning on the tax package, the special committee began urging member companies to write to the president with the messge that the continuation of DISC is vital to helping American business in overseas markets.

The answers coming back, as Lee tells it, are the form letters. In that atmosphere, the special committee is mobilizing to get its way in Congress.

The scene now developing on Capitol Hill is familiar -- scads of letters to member of Congress, visits and offers of more information, data about the impact of the DISC subsidy in member's home districts.

With more than 9,000 DISCS in existence, the program touches virtually every congressional district in the counrty. It ranges from the huge General Electric Co., a major beneficiary of the tax break, down to small independent companies just getting into exports.

Beyond that, the special committee is generating support in other quarters. From his office at the law firm of Steptoe and Johnson in downtown Washington, Bill Lee keeps close track of -- and helps stimulate -- the support.

He produces documents showing that the National Governors Conference has gone on record in support of some kind of special federal help to exporting companies.

He has copies of a pro-DISC resolution passed by the Building and Construction Trades Department of the AFL-CIO, which shows that the labor alliance's official opposition to DISC is not as uniform as George Meany may believe.

For showing to workers in plants that might be affected by a change in the federal tax policy, the special committee has prepared film strips that tell them in cartoon fashion how DISC benefits them.

And already, spurred by the legislative "alerts" issued by the special committee, executives of companies that have set up DISCS are peppering member of Congress with letters warning of dire economic results if the export subsidy is ended.

From the perspective of Bill Pietz and Robert Brandon from the Public Citizen Tax Reform Research Group, that kind of lobbying is virtually impossible to overcome because of the job-lss anxieties it creates in the mind of a congressman.

Rep. Abner Mikva (D-ILl.), an opponent of DISC, commented on the technique:

"they've learned that business only has so much clout, so they broaden their base. Employes write in and say they'll lose their jobs if we end this. Last time, the letters were incredible. They were very well-targeted -- letters even came from blue-collar workers in my district, and there aren't very many of them, supporting DISC."

Mikva continued, "that becomes very persuasive because of the coalition they've built. There is no one left for the reform except the poor Treasury Department and a couple of economists who are left standing naked . . . They don't ofer people anything. They appeal to concerns and fears and anxieties. Most of them don't even contribute to your campaign."

Bill Lee sees it in different, and rather more dramatic, terms: "The lines are drawn. The president has his guns. We have our guns. We are now in a shooting war."