The Senate Finance Committee yesterday reaffirmed, in scaled-down form, a proposal to throw a larger share of Social Security payroll taxes on employers than on their employees.

The committee adopted a proposal by Gaylord Nelson (D-Wis.) to make employers pay the Social Security tax on the first $50,000 of an employee's annual earnings from 1979 to 1984 and on the first $75,000 from 1985 on - while the workers themselves are paying on a much smaller portion of wages.

The committee had previously accepted a Nelson plan to make employers pay on the first $100,000 but Nelson cut it back yesterday because of objections that the burden would be too heavy for many firms. The reduction enabled Nelson to ward off a proposal by Carl T. Curtis (R-Neb.) to scrap the plan altogether.

The overall Social Security financing bill, with numerous other financial provisions, is expected to win final committee approval next week.

The Nelson amendment means that employers would pay $30 billion to $35 billion more in Social Security taxes than employees over the next half decade or so - breaking for the first time the traditional "parity rule" under which employers and workers have paid exactly the same amount of taxes since the system began. At present, employers and employees each pay 5.85 per cent of the first $16,500 of a worker's wages.

The Nelson language was part of an omnibus Social Security bill which the leadership hopes to bring to the floor before the end of the current session in order to shore up the old-age and disability trust funds, now in shaky condition.

By loading a larger portion of costs onto business firms and other employers, the Nelson proposal would allow smaller tax increases for workers than would otherwise be required. A House Way and Means Committee bill scheduled to come to the House floor concept, and has much bigger eventual payroll tax increases for higher-income workers than the Nelson plan.

Before reapproving the Nelson amendment with the new, scaled-down figures, the finance Committee rejected on a 9 to 9 tie a proposal by Curtis to raise the extra money needed for the old-age and disability funds by retaining the parity concept and raising the tax rates for workers considerably more than under Nelson's plan. Attacking the Nelson plan as a "soak-the-employer" proposal, Curtis won the support of all seven committee Republicans, Harry Byrd and (Ind Va) and Herman Talmadge (D-Ga), but nine democrats voted against his substitute.

Nelson also won committee approval of a "fiscal relief" plan for state and local governments and non-profit organizations whose Social Security tax payments would go up because of their increased obligations under the $50,000/$75,000 proposal. Under Nelson's "fiscal relief" language, state and local governments and nonprofit organizations would receive from the Treasury an amount equal to half their extra payments each year - for a total of $32 billion in such Treasury payments over the next nine years.

Other key provisions of Nelson's overall financing plan for Social Security, already approved at previous sessions:

Raise the Social Security tax rate for employers and employees from the 6.02 per cent already scheduled for 1978 under current law to 6 135 per cent in 1979-80, 6.6 per cent in 1981-84, 7 per cent in 1985, 7.05 per cent from 1986 to 1989 and in stages to 8.9 per cent by 2011.

Raise the wage base for employees scheduled to go to $17 000 next year, in stages to $33,900 by 1987, this means that the maximum tax on the highest paid employee, which is $965 this year, willbe $2,390 for those making $33,900 or more in 1987.

Rewrite the long range benefit formula, to wipe out a quirk that was driving future benefits sharply upward so that the average retiree will receive benefits when he first retires equal to about 43 per cent of his wages subject to Social Security in the last year before he retired.

Permit retirees to earn up to $4,500 in 1978 and $6,000 annually thereafter without loss of benefits. The current limit is $3,000.