The Carter administration won't be asking organized labor to hold wage increase for 1978 below the average rise for 1976-77, as policy makers had indicated earlier.

Instead, officials say, unions will be urged to keep the average increase over the life of any contract signed this year below the average rise for the previous contract - even if the earlier settlement covered three of more years.

The definition was broadened to prevent any distortions that might arise from applying the earlier 1976-77 rule of thumb to multi-year union contracts.

Union settlements often are front- or back-loaded to concentrate most of the increase in the first or last year of the three-year contract. Using a 1976-77 base in such cases could throw off any reasonable appraisal.

Charles L. Schulze, chairman of the president's Council of Economic Advisers, announced the 1976-1977 rule of thumb when the administration unveiled its anti-inflation program last month, saying the White House would try to persuade business and labor to "decelerate" price and wage increases from their average of those two years.

Yesterday, however, top administration inflation-fighters said the 1976-77 rule would apply only to non-union wage increases. New Union contracts would be compared with old ones. Fringe benefits and escalator clauses would be considered part of the overall settlement package.

The administration repeatedly has insisted that it is not setting down any numerical wage or price guidelines, but only wants to see wages and prices "decelerate" from their previous pace. The 1976-1977 rule of thumb was provided in answer to the question: Decelerate from what?