With barely a ripple of public notice, the House and the Senate have voted to make room in their 1978 budgets for a $250 tax credit for families saddled with college tuition costs.

But so far, at least, the votes reflect little more than a rhetorical exercise, since both houses would have to pass specific tax-cut legislation before the credit, which ultimately could cost the government $2 million a year, could take effect.

And budget experts in both the House and Senate yesterday gave such legislation little chance of enactment this year.

In four, of the past five Congresses, the Senate has approved tuition tax credits in the form of amendments to other bills, but each time they have been excised quietly in conference.

This time, after the Senate by voice vote made room in the budget for $175 million worth of tuition credits, Finance Committee Chairman Russell B. Long (D-La.) let it be known he probably would encounter difficulty finding a bill to which the measure could be attached as an amendment.

The House, in a surprise 311-to-76 vote, also has made room in its binding $459.6 billion budget for tuition credits.

But Rep. Al Ullman (D-Ore.), chairman of the Ways and Means Committee, reportedly is so firmly opposed to the plan that he has balked at scheduling hearings on the issue, much less letting it go to a floor vote. His precessor on Ways and Means, Wilbur Mills, was equally adamant about it, and the perennial tuition creidt bill has a long history of languishing in committee.

Opposition to the proposal generally has centered on its cost, which critics say would total $1 billion in the first four years, rising to $2 billion a year after that when the tax credit would be raised to $500.

Moreover, opponents argue it provides a quick windfall for the upper half of the income scale, while denying tax relief to pockets of need. Other critics point out that instead of simplifying tax returns, tuition allowances - coupled with credits for such expenditures as home insulation - would make more of a morass of the tax law.

If anyone is expecting the Carter administration to champion the cause of tuition credits, they should look elsewhere.

When the House Budget Committee held hearings last spring, officials of Treasury and Health, Education and Welfare spoke forcibly against tuition credits, and administration sources say such allowances will not be included in the pending tax overhaul proposals.

Budget Committee officials in both the House and Senate ysterday interpreted the votes to include tuition credits in the budget resolutions as rhetorical expressions or "show boating."

"It's a way they could vote for it without a lot of contentin over it. They knew they weren't authorizing anything, and it was clear the leadership wouldn't go for it," said a Senate Finance Committee staff member.

Nevertheless, Rep. Lawrence Coughlin (R-Pa.), sponsor of the tuition amendment to the House budget resolution, plans to continue pushing Ways and Means on the issue, his aides said.

"Ullman could not have let it go to a floor vote last year, because he knew it would pass. This (House vote) just increases the pressure on him. It enhances its chances of it passing eventually," a Coughlin aide said.