House-Senate conferees reportedly agreed yesterday on a plan for sending the big Social Security tax bill to the President this week, stripped of a college tuition tax credit provision that has held it up.

Under the likeliest version of this plan, the Senate-passed tuition credit would then be put to a separate vote in the House, and if it passed there, would be sent to the President to be signed or vetoed on its own merits.

The administration opposes the credit, but wants the Social Security bill.

In another development yesterday, there was the first small sign of movement in the House-senate conference on natural gas pricing. But Sen. J. Bennett Johnston (D-La.), chief spokesman for those seeking to lift gas price controls, said he had given up all hope of getting agreement on a gas bill by Christmas.

The Social Security conferees had agreed last week on new payroll taxes totaling $227 billion over the next decade. But they broke up Friday in disagreement over a Senate provision for annual tax credits of $250 to help pay escalating college costs. The eight Senate conferees were unanimous in supporting the credit authored by Sen. William V. Roth Jr. (R-Del.). But Senate support for Roth began to crumble as administration pressure for release of the Social Security bill increased.

After a caucus of the Senate Finance Committee yesterday, chairman Russell B. Long (D-La.) said he expects, the Social Security issue to be resolved today. He would not say how.

House sources said agreement has been worked out with the conferees and the White House on an unusual procedure to free the Social Security bill that President Carter urgently wants and also give Roth a House vote on his tax credit.

The plant which conferees are expected to approve today is to drop the tax credit from the Social Security bill. The Senate would then attach the credit to a minor House passed tariff bill and send it back to the House for a vote Thursday. The House would bote on both the Social Security and tax credit measures Thursday and Carter could veto the tax credit hill if he chose without also killing the Social Security bill.

Roth did not attend the Finance Committee meeting yesterday but kept in touch by telephone. He said yesterday afternoon that as far as he was concerned, no final agreement had been worked out among Senate conferees. He said he was optimistic that a solution would be found and that separating the two issues into separate bills was the approach most talked about.Roth said that would be acceptable to him.

On natural gas. House conferees tried to break a stalemate by making the Senate an offer than would satisfy some of the non price fears of producing states but does not deal with the basic issues of regulation, price levels, control of the intrastate market and definition of new gas eligible for a higher price.

Carter proposed continuing price controls on natural gas shipped across state lines, raising the price ceiling from $1.46 to $1.75 per thousand cubic feet (MCF) with future increases to cover inflation, and extending controls to gas consumed in the state where produced. The House approved this, but the senate voted to lift controls.

To meet the fear of producing states that federal control of the intrastate market might take away their gas, the House conferees offered to forbid federal allocation of intrastate gas. This means federal officials could not order gas produced and consumed under contract in Texas to be diverted to interstate pipelines to meet northern shortages.