Health, Education and Welfare Secretary Joseph A. Califano Jr. yesterday, threatened to recommend a veto of the Social Security bill if it is sent to President Carter with a controversial tuition tax credit still attached.

At a White House news conference, Califano said the tuition provision's sponsor, Sen. William V. Roth (R-Del.), "is holding the viability of the Social Security system hostage for a $1.25 billion ransom which would go to some of the wealthiest people in America . . .

"That proposal is utterly irrelevant to the Social Security legislation."

Later, he added, "If this kind of an amendment stayed in this legislation, I would be concerned enough to seriously consider recommending a veto."

The amendment that so provoked Califano's ire was attached to the Social Security bill on the Senate floor. It would provide families a $250 tax credit for each child attending college.

It is attached a major Social Security bill, urgently sought by Carter, that would provide up to $227 billion in new taxes over the next decade to finance the ailing system.

After weeks of debate, House and Senate conferees agreed Friday evening on the largest peacetime tax incrase in U.S. history to keep Social Security trust funds from dipping so low that full benefits could not be paid.

But the agreement soon foundered when the House conferees refused to go along with the Senate's tuition credit plan.

The plan's supporters argue that the tuition credits would help hard-pressed middle-class Americans, the bearers of the largest tax burden.

Califano countered that families with dependents in colege earn an average of 50 per cent more than the median income - $22,000 vs. $14,500.

"This money would go to the wealthiest doctors, lawyers, and others, who have children in college, because it's not directed where it's needed," he said. "But the most important point is that it's an absolutely incoherent way to make educational policy in this country."

Roth's office had no one answering telephone calls yesterday.