The Carter administration opened the defense of its controversial Social Security financing proposals before a skeptical Senate subcommittee yesterday, and immediately ran into opposition from Finance Committee Chairman Russell B. Long (D-La.).

Long took strong exception to the proposal presented by Secretary of Health, Education and Welfare Joseph A. Califano Jr. to take $14.1 billion from the Treasury's general, or income tax, revenues over the next five years and put it into the Social Security trust funds to prevent them from running out of money. Up to now Social Security has been financed by a specific earmarked Social Security payroll tax without any general income tax revenues.

"We don't have any general revenues to finance it with," said Long, asserting that the federal budget is already at a $60 billion annual deficit.

"Reaching for general funds when no general funds are there," said Long, is "to resort to the printing press" in order to pay debts.

Asked how he would handle it, Long said later that "I think you ought to put enough Social Security tases on to pay for it."

Califano, explaining that the diversion of Treasury funds into Social Security would occur only when Social Security tax collections are low because unemployment is higher than 6 per cent, said, "We're only talking about $14 billion . . . over a five-year period."

A second unprecedented administration proposal - to require employers (but not employees) to pay taxes on a worker's entire earnings not just the first $10,500 a year, also ran into criticism.

Califano stressed that removing the ceiling on taxable wages on which employers pay the Social Security tax wouldn't mean any net tax increase for most small employers because most of them have relatively low-paid employees who are blow the ceiling. The extra employer taxers would fall largely on bigger firms with a high percentage of employees above the current ceilings, he said.

Chairman Gaylord Nelson (D-Wis.) of the Social Security financing subcommittee, opened the hearing by explaining the basic immediate problem: the Social Security trust funds for old-age and disability benefits are simply not collecting enough from the present payroll tax to pay for benefits. Over the next five years, they ned to raise an added $83 billion to stay in good shape.

The extra $83 billion is in addition to what will be collected under present law.