The Senate, caught in a heavy crossfire between business and labor lobbyists, took up the administration's labor law revision bill yesterday and found itself moving inexorably toward a filibuster, perhaps a long one.

Conservative opponents of the union-championed measure said they had speeches prepared to last through the Fourth of July and would talk until Labor Day, if necessary, to block the measure.

But debate began in a desultory fashion, with the bill's backers saying they will eventually have the 60 votes necessary to close off debate and bring it to a vote, possibly in a couple of weeks.

The bill is simply designed to "end delay and bring an end to the growing number of violations of employe rights" in organizing unions and winning contracts, said Senate Human Resources Chairman Harrison A. Williams (D-N.J.)

It is an "overbroad solution to an exaggerated problem" that would smother small businesses and upset the current balance in labor-management relations, said Senate Minority Leader Howard H. Baker Jr. (R-Tenn.)

There was little drama to the birth of this filibuster: no delaying tactics, no cots, no baggy eyes, only long and generally predictable speeched from both sides that sounded like a routine warm-up for a vote. The Senate stopped talking before sundown and was not scheduled to resume again until midday today.

But there was hints of things to come, with Sen. Jesse A. Helms (R-N.C.) summoning up visions of a "Snowbelt [vs.] Sunbelt" civil war to "unionize the South by federal force," and Sen. Strom Thurmond (R.S.C.) pledging to "fight this bill and fight it to the last."

Meanwhile the Senate Democratic leadership hunkered down for another long siege after the 10-week Panama Canal debate, saying it will not withdraw the labor bill no matter how long it takes to get it passed.

At the same time, opponents prepared to fight on even in their first filibuster is cut off, by offering 500 or more amendments to the bill and then by filibuster whatever comes out of a House-Senate conference on the proposal.

The House passed a somewhat stronger version of the Senate's bill last October, 247 to 163. But that was before business groups marshaled forces for what AFL-CIO President George Meany has called a "holy war" against unions, which have made the bill their top priority for this session of Congress.

The result has been a multimillion-dollar lobbying campaign by both sides, one of the most intense in history, according to many senators who also concede that general public interest in the bill, outside of the business and labor community, is marginal.

President Carter has also pointedly reaffirmed his support for the measure, making it another test of the administration in Congress as wall as a key element in his sometimes shaky relations with organized labor. Labor is counting on Carter's help as time goes on to get the bill passed.

The bill, drafted jointly by the White House and the AFL-CIO, would set deadlines of from 30 to 75 days for union representation elections, require time-and-a-half back pay for workers fired illegally for union organizing and compensation for wages lost during illegal bargaining delays, permit the government to deny contracts to repeated labor law violators and let unions campaign on company property if employers do so.