The White House will delay submitting a tax simplification bill to Congress for several months, Republican congressional leaders said yesterday after meeting for an hour with President Reagan.

Sen. Bob Packwood (R-Ore.), chairman of the Senate Finance Committee, said it was the unanimous recommendation of the Republican members of his committee and the House Ways and Means Committee that the tax proposal should wait until Congress has dealt with a budget plan that would cut federal spending by $51 billion.

"The point was made forcibly that many of the allies we need on spending cuts are going to be enemies on the tax bill," he said.

He said it would be possible for Congress to pass a spending-cut package and the tax bill by Aug. 1, but added that, if the tax bill was pushed simultaneously, "you drain off so much support that you don't get the spending cuts."

The Republican leaders said that Treasury Secretary Donald T. Regan, who is to become White House chief of staff next month, had told them it would be weeks, perhaps months, before the administration submitted a tax bill.

"I would predict we will not see a Treasury and/or White House tax bill for at least two, maybe three, months," said Sen. John Heinz (R-Pa.) "Indeed, I will predict that the administration will not send us a bill until after the spending-cut decisions have been made by the Senate and maybe by the entire Congress."

Until yesterday, White House officials had taken the position that the tax simplification plan would be sent to Congress in March, about a month after the president presents his budget proposal.

Packwood said the uniform advice of the Republicans was "spending cuts, spending cuts, spending cuts."

But administration officials said the GOP congressmen were advising Reagan to follow the strategy he already is using.

White House deputy press secretary Marlin M. Fitzwater, repeating words used by White House chief of staff James A. Baker III, said that budget and tax bills were "of equal priority but on different tracks."

He said that the budget timetable required the administration to focus first on spending decisions and that the target was still to submit a tax simplification bill to Congress during March.

Nonetheless, the view expressed by the members of Congress yesterday was that the timetable for tax simplification has slipped. Privately, some administration officials have acknowledged that such slippage could cause delay of tax simplification until 1986.

Sen. John C. Danforth (R-Mo.) said Heinz told the president that tax simplification was like motherhood and added, "If tax simplification is like motherhood, I think there are a lot of people in the country who are interested in mugging Mom."

Reagan, as usual, kept his own counsel. "The president by and large listened and did not specifically respond one way or the other," Packwood said.

Packwood and Danforth expressed the view that most senators want to cut defense more than the $8.7 billion that Reagan has recommended. But they said the defense budget was not a focus of the meeting yesterday.

Earlier in the day the president met with a dozen representatives of banking, savings and loan, Realtor and homebuilder organizations and asked them to support his budget plan.

In a 20-minute meeting, Reagan thanked the executives for their support and added, "We're going to be asking you for a great deal more."