Senate Majority Leader Robert Byrd yesterday wrote off the possibility of any tax cut before the November election, saying he will not bring a proposed $39.8 million package to the Senate floor. He said the decision has the "overwhelming" support of Democratic senators but acknowledged that Republicans will fight to get the measure passed.

A tax cut now would endanger the current economic recovery and would be seen by the public as "pure political gimmickry," Byrd said. Debate in any case would be "an excerise in futility," he continued, because House leaders have refused to consider the measure now and President Carter has said he would not sign it before Nov. 4.

However, the West Virginia Democrat told his regular Saturday news conference that the pending bill is a good one and that there would be a "much improved" climate for it in the lame-duck session after Nov. 4. He flatly predicted a tax cut by early next year, but said he would like to see a smaller version than the pending Senate Finance Committee package.

Byrd had wrangled with Finance Committee Chairman Russell Long (D-La.) over scheduling the measure, and Long said yesterday he would support an expected Republican attempt to attach the tax cut to another piece of pending legislation in order to get a vote before the elections.

"I'm ready to go, ready to bring it up tomorrow," Long said, "but I'm not going to try to force it to a vote" by offering an amendment personally. A task force from Long's committee drew up the package in response to a Senate Democrats' resolution demanding to GOP tax initiatives in June.Committee members tried to please Byrd by stripping the package of special-interest "Christmas tree" provisions, and a group led by Long and task force chief Lloyd Bentsen (D-Tex.) appealed to Byrd last week to let the Senate vote on it.

The measure would provide $22.3 billion in tax cuts for individuals and about $17.5 million in reduced taxes for businesses. Byrd agreed that injecting that much money into the economy would push up interest rates, create "an inflationary psychology" and disrupt financial markets, just as economic indicators are beginning to show signs of health.

"It appears the recession has bottomed out," he said.

Republicans seemed delighted to pick up the challenge.

"Ronald Reagan will support any rational and serious effort to cut the rate of tax increases," said Lyn Nofzinger, press secretary for the GOP presidential nominee. "It's a shame Byrd is putting his loyalty to Jimmy Carter above the needs of the country." President Carter supports a $27 million tax cut version but not before Nov. 4.

Rep. Guy Vander Jagt (Mich.), chairman of the Republican Congressional Campaign Committee, said Byrd's move would be "an enormous help" to GOP candidates. "It symbolizes the inability of the Democrats to govern. They don't want to make the hard decisions before the election," he said.

Sen. Robert Dole (R-Kan.) promised to offer the committee bill as an amendment to any revenue bill that comesup before the session ends Oct. 2, a date Byrd set yesterday. "I'm disappointed in [Byrd's] decision," he said. "I think it was based more on politics than on economics." Suitable vehicles for the amendment, he said, might include unemployment insurance changes or reallocation of part of the Social Security tax.

Byrd told his news conference that Republicans have jumped to support Long's bill because their own tax bill is "a deep hole . . . an albatross. Now they want to use the Finance Committee bill to bail out Mr. Reagan." Reagan has backed a tax proposal written by Sen. William V. Roth (R-Del.) and Rep. Jack Kemp (R-N.Y.), that includes a 10 percent across-the-board cut.

Rep. James C. Corman (Calif.), head of the Democratic Congressional Campaign Committee, said he was very pleased at Byrd's announcement and said it would help Democrats get elected nationwide.

Byrd was also optimistic about political matters. "I don't think the Repulbican Party has a chance, not a chance, of taking over the leadership of the Congress," he said. Democrats stand to pick up Senate seats in Oklahoma, Pennsylvania and New York, he said, and to retain seats in Connecticut and Illinois.

He added that a backlash had developed against what he called "false, distorted literature" from right-wing groups and that several of their Democratic targets now appeared to be in much better shape politically, including Sens. Frank Church of Idaho, Gary Hart of Colorado, George McGovern of South Dakota and John Culver of Iowa.