In a lobbying battle that apparently knows no bounds, American business and labor are slugging it out in a Senate office building basement with truckloads of mail that - if truth be known - scarely a soul is reading.

The issue is revision of labor laws, not the flag-waving, tears-to-the eyes and lump-to-the-throat kind of issue that would normally send off a paper gusher in the Senate mail room in the Dirksen Office Building.

But it has done so, thanks to a game of lobbying one-ups manship being played by business groups and labor unions. The groups now have a new measure of lobbying effectiveness: gross tonnage.

"It's tremendous proliferation of waste," concedes Victor Kamber, director of the AFL CIO's labor law revision task force, whose troops are responsible fore nearly half the roughly 2 million pieces of mail that the lobbying confrontation has unleashed. There is plenty more to come.

Business lobbying groups proved the worth of the postcard bitzkrieg in earlier battles over labor legislation, so the AFL-CIO and other unions decided to prepare a defensive arsenal equipped to deliver postcard for postcard, according to Kamber.

"Some members (of the Senate) weigh the mail," said Kamber, "and we've got to sure if balances our way."

Mail inspired by the National Action Committee on Labor Law Reform, which is coordinating business opposition to the revision, dominated the scene in January. But union postcards are now beginning to pour in about 700,000 so far, with another 760,000 singed postcards held in reserve at the AFL-CIO headquarters for when the need arises.

"When a Senate office calls and complains about a lack of mail from us, we'll deliver," said Kamber.

The administration's revision bill, which passed the House last year, would set deadlines for holding union representation elections and stiffen penalties for employers who thwart union collective bargaining drives.

Proponents call it a "moderate" proposal, largely procedural in nature, but groups such as the U.S. Chamber of Commerce contend that it would tip the scales in favor of unions and lead to a tripling of union membership - from 20 to 60 per cent of the work force over the next decade. They say it is the opening wedge to "compulsory unionism," a charge that the unions and the administration deny.

The campaign against the bill has struck such an emotional chord, especially among conservatives and small business people, that labor law mail is outstripping Panama Canal mail in many offices.

Kamber said an aide to Sen. Edward M. Kennedy (D-Mass.) said the Senator's weekly mail is running 3,600 pieces of labor law to 82 pieces on the canal. He said the office of Sen. Lowell P. Weicker (R-Conn.) has started counting labor law mail by the box rather than individually.

At a rally yesterday in the Dirksen Office Building, th bill's proponents conceded that they will lack the 60 votes necessary to break an expected filibuster when the measure comes up on the Senate floor, after the canal treaties are acted on. Action on the treaties may not come until late March.

Sen. Jacob Javits (R-N.Y.), a consponsor of the bill, said the lobbying campaign against the bill has been "amazing in light of the fact that it (the bill) doesn't do that much." He speculated that union foes are "smelling blood" because of last year's defeat of the common-site picketing bill and because of declining union membership. There is a "critical need," he said, for more grassroots support for the measure.

If that wasn't gloomy enough for the bill's backers, Sen. Harrison A. Williams (D-N.J.), the other consponsor, said that, even if a filibuster is broken, the bill's foes could tie it up in the Senate so long with amendments that the leadership might be forced to pull back the bill.