Senate leaders, acting swifty to comply with President Carter's new position on the tax bill, yesterday delayed floor action on the bill pending Finance Committee action today to strip out the $50-per-person rebate that carter no longer favors.

Finance Committee Chairman Russel B. long (D-La.) told the Senate the committee will indoubtedly kill the rebate by a wide nargin today.

But Long and several others hinted that the committee might refuse a second presidential request to kill a proposed increase in the investment tax credit for business. Several committee members believe that retention of that investment credit, which would save businesses $900 million in taxes this fiscal year and $2.4 billion next, is economically justified.

They believe Carter asked that it also be jettisoned only because it would anger taxpayers to lose their $50 rebate while seeing businesses get an extra tax break.

In January, convinced that the economy needed a speedy spur, the President requested that each taxpayer receive a refund of $50 for himself and each dependent on taxes paid for 1976 - a rebate that would have pumped $10.4 billion into the economy by Oct. 1.

However, facing a tough fight in the Senate and warnings from some aides that the rebate might prove unnecessary or inflationary, Carter last week ababdoned the rebate and the business investment tax credit increase.

The House already had passed the tax bill and the Senate was due to begin debate yesterday. In the light of the President's request, the bill was postponed but left on the floor until the Finance Committee could vote on a recommended floor amendment taking care of carter's requests.

Floor debate is expected to begin shortly after the Finance Committee acts. Several different groups of Republicans, convinced that a permanent reduction of personal income tax rates is needed to spur the economy, apparently plan to offer floor amendments for permanent cuts in place of the abandoned rebate, though the total tax loss from these would be far less than from a rebate.

Sen. William V. Roth (R-Del.), according to aides, will offer his amendment cutting personal income tax rates by 10 per cent across the board. This would reduce the top rate from 70 to 63 per cent, and the bottom rate from 14 to 12.6 per cent, at a loss of $6 billion this year.

A more modest rate cut, ranging from 4 to 14 per cent for those with taxable income of less than $20,000, will be offered by a group headed by Jabcob K. Javits (R-N.Y.), as things look now. Its impact this year would be $2.5 billion, but that would rise to $9.4 billion next year.

Sponsors of these amendments argued all along that a permanent, personal rate cut would have a permanent long-range stimulative effect on jobs and economic growth, while a rebate would not.

Although the rebate was the biggest item in the tax bill, it also contains other important provisions. The standard deduction (for those who don't itemize), which now ranges from $1,7000 to $2,400 foindividuals and from $2,100 to $2,800 for couples, would be set at $2,200 for a single person and $3,200 for a couple or head of household. Forms would be simplified so that 96 per cent of all taxpayers would be able to use the tax tables.

The $35 individual tax credit, the 10 per cent "earned income credit" for low-income families less than $4,000) and businesses would be extended one year to the end of 1978. Reductions in the amount of sick pay and overseas earnings that can be exluded from taxable income would apply starting with taxable year 1977 instead of 1976.