Hale Champion, 55, under secretary of the Health, Education and Welfare Department, will soon be named commissioner of Social Security, according to authoritative sources on Capitol Hill.

Sources said the leading candidate to replace Champion as under secretary appears to be Stanford G. Ross, 46, a partner in the tax-law firm of Caplin and Drysdale and a friend and former Johnson administration associate of HEW Secretary Joseph A. Califano Jr.

"Ross is probable but not certain," said a Capitol Hill source.

Ross was a Califano classmate at Harvard Law School, served under him in the Johnson White House in 1967-8, and has had a variety of government posts during dating to 1961.

Although commissioner of Social Security is technically a "lower" job than under secretary, many consider it the second most important job in HEW.

The commissioner administers two-thirds of the HEW budget - Social Security, welfare and aid to the aged, blind and disabled - and nearly two-thirds of the departmentp's employes.The Social Security Administration handles cash payments of about $115 billion a year to more than $40 million persons, and it has more than 80,000 of the department's 144,000 employes.

The commissioner post has been vacant since James B. Cardwell retired at the end of 1977. Don Wortman, acting commissioner, will remain as deptuy, sources said. The commissioner and under secretary are both subject to Sentate confirmation.

In the temendous scope of Social Security Administration operations, "a 1 percent error in Social Security costs $1 billion," said one official.

Champion is a former newspaper reporter (Milwaukee Journal. Sacramento Bee, San Francisco Chroicle who was prss secretary in 1959-60 when Edmund G. Brown was governor of California. He was state finance director from 1961 to 1966 and financial vice president of Harvard for six years before coming to HEW in 1977. He has been working on health programs and related matters. He declined to discuss his impending appointment yesterday.

Ross in addition to practicing law is chairman of the Advisory Council on Social Security, citizens and welfare professionals who help advise the government on Social Security policy.He attended Washington University in St. Louis and Harvard Law.