With the year just over 48 hours old, a new cast of jumping numbers has danced onto center stage, with little applause expected from America's hirers and toilers.

Called Risers, the show will run through year's end and is to be succeeded by Risers II in 1981. The members of the cast:

Social Security -- The weekly tax has risen to 6.65 percent from 6.13 percent; the maximum annual payment to $1,975.05 from $1,587.67, and the maximum salary on which it is levied to $29,700 a year from $25,900. Wage earners in the $10,000- to $20,000-a-year range who didn't see an increase in their Social Security tax a year ago are seeing it now.

Minimum Wage -- Affecting an estimated 5.6 million workers, the federal minimum wage is now $3.35 an hour, up 25 cents from last year. In 1979, the minimum hourly wage was $2.90.

Zip Code -- Starting in June, the Postal Service will have devised a nine-digit zip code for every business in the country, and by Oct. 1 expects all businesses and households to have a number that is four digits longer than the current codes, an 80 percent increase in length.