The Senate Finance Committee voted unanimously yesterday to keep alive for an extra year two tax breaks Congress supposedly killed last fall, one affecting sick pay and the other covering income earned abroad.

The committee also agreed on a tax cut for business that is a compromise between what President Cartr proposed in January and what the House approved last week.

Under the compromise, mainly the work of Sen. Lloyd M. Bentsen Jr. (D-Tex.), businesses would have a choice between two credits, or reductions in taxes owed for the next two years - an increased investment credit for buying new machinery, or a new employment credit for hiring additional workers.

Carter is pressing for the higher investment credit, which many of the nation's larger, more capital-intensive corporations also want, but the House approved an employment credit instead.

The Finance Committee is voting on the tax-cut legislation Carter proposed to pep up the economy. The committee put off until today decisions on the individual tax cuts the President recommended, including the $8.6 billion he wants to send out this spring in rebates of 1976 income taxes.

Many in Congress doubt the rebate will do the economy much good, and a Republican proposal to replace it with a "permanent" tax cut barely lost in the House last week, 219 to 194. There is a similar lack of enthusiasm for the rebate on the Finance Committee, and Republicans there will also propose a permanent tax cut as an alternative. But yesterday's betting was that the rebate will narrowly survive.

The provisions affecting sick pay and income earned abroad were part of last year's tax "reform" legislation, approved in late fall.

Previous law had allowed tax payers to exclude or deduct from taxable income up to $100 a week or $5,200 a year in sick pay if they were absent from work a sufficient length of time because of illness or injury.

The reform legislation narrowed this exclusion, saying it could only be taken by taxpayers who were under 65, permanently and totally disabled and in the lower and middle income brackets. To help hit the revenue-raising target Congress had set for tax reform, this change in the law was made retroactive to Jan. 1, 1976.

That retroactive effective date added to the outcry that always accompanies loss of a tax break, and the congressional budget committees have since relented a little so the effective date could be moved to Jan. 1 of this year. That is what the Finance Committee voted to do. The new date, if it stays in the bill, will benefit 1.2 million taxpayers, and cost the Treasury $327 million this fiscal year.

Presumably the eligible taxpayers will have to file amended returns later in the year. Many taxpayers have already completed their 1976 returns, and the 1976 tax forms make no provision for the old-style sick pay exclusion anyway; they were changed to reflect the tax reform legislation.

All these things are also true for income earned abroad. Previous law excluded $20,000 of such income from taxation. Congress last year reduced this to $15,000 effective Jan. 1, 1976, and the Finance Committee voted yesterday to move that to Jan. 1, 1977, at a cost to the Treasury this fiscal year of $38 million. An estimated 100,000 taxpayers would gain from this change.

The business provisions approved by the committee would lift the investment tax credit from the present 10 per cent of the cost of new machinery to 12 per cent. As an alternative, a business could claim as a credit 25 per cent of the first $4,200 in wages paid all employees hired in excess of normal growth, defined as 3 per cent a year. The House bill limited this credit to $40,000 per business, but the Bentsen proposal approved yesterday contains no limit.

The two business proposals taken together would cost the Treasury an estimated $2.4 billion next fiscal year, half in investment and half in employment credit.

Yesterday committee members Floyd K. Haskell (D-Colo.) and Spark M. Matsunaga (D-Hawaii), joined by Ralph Nader and two small business organizations, served notice they will fight the investment credit plan on the Senate floor.

They noted that just five companies - American Telephone & Telegraph, Exxon, General Motors, Goodyear and U.S. Steel - received more than $1 billion in investment credits in 1975 - more than 20 per cent of the investment credits that went to all corporations in that year.