The second day of the House sub-committee hearings on extending the Equal Rights Amendment ratification deadline yesterday signaled an emerging new battleground in the ERA fight - Congress.

For five years, state legislators have tangled over the divisive and emotional issue of ratifying the ERA. It is now doubtful that the necessary three more states will ratify the amendment by the current March 22, 1979, deadline.

So now the debate is on whether or not Congress has the right to extend that deadline. And this issue immediately raises a question of vital political concern to those on both sides of the ERA issue - whether it is legal for states to rescind ratification. Of 35 that have ratified, three - Idaho. Nebraska and Tennessee - have since voted to rescind.

This is the situation:

Rep. Elizabeth Holtzman (D.N.Y.) has introduced a bill to extend ratification deadline for seven years until 1986.

In two hearings before the House Subcommittee on Constitutional Rights this week, constitutional lawyers and Justice Department witnesses have agreed that Congress has a right to extend the deadline. Next week's witnesses, however, are expected to argue the opposite.

.Even those who agree on the right of Congress to extend the deadline, disagree on how it can do this. Yesterday's two witnesses, Yale Law School professors and leading constitutional authorities Charles L. Black Jr. and Thomas I. Emerson, squared off on the key points that are certain to be raised and argued again and again before Congress votes on this issue.

Emerson went along with previous testimony that Congress could extend the deadline by a majoritynce the ERA was passed by a two-thirds majority in 1972, the deadline change would also take a two-thirds majority.

Regarding rescission, several witnesses have argued that either states have no right to rescind or that the matter will have to be to decided by the Congress sitting at the time 38 states have ratified. "Congress has consistently accepted the view, in the case of the 14th, 15th and 19th. Amendments that a state may not rescind. I believe this is the correct position." said Emerson.

But Black replied that in the case of the 14th Amendment. Congress already had the requisite 28 states before making a decision on whether states could rescind. He does not see how the amendment would be valid if, for example, the requisite 38 states ratified but three of those states had rescinded.

"No amendment has ever passed without three-fourths unrescinded ratifications. If you can "rescind" the seven-year limitation it is very hard for anyone to argue with a straight fact that recission is not available to the states," he said.

Yesterday's session was characterized by a sharp exchange between Holtzman and Black over these issues. Holtzman later said she was confident there were enough votes for a majority and I would suspect we could master the two-thirds if necessary.

The subcommittee hopes the bill will reach the floor next spring.