The Senate Finance Committee appeared ready to approve a series of business tax credits to encourage energy savings yesterday when Sen. John C. Danforth (R-Mo.) spoiled the fun by asking what it would cost.

Assistant Treasury Secretary Laurence Woodworth, administration spokesman at the meetings where the committee has dismantled President Carter's proposed energy tax program, said his estimates showed it would cost $15 billion in lost revenue by 1985 at an energy savings of only 20,000 barrels per day. By contrast, the home insulation tax credit program is expected to save 300,000 barrels a day by 1985 at a cost of $5.7 billion.

"I don't think you can justify this on the basis of saving," said Woodworth.

"I thought I was for it, but I've changed my mind," said committee chairman Russell B. Long (D-La.).

The committee staff, which has complied a list of every conceivable tax credit that might save energy, was directed to go back to the computer and try to determine how much each of the proposals made by various members of the committee will cost in dollars and save in barrels of oil.

Regardless of the initial balk at the laundry list of energy tax breaks, the Senate panel eventually gave its tentative approval to a five year, $3.3 billion series of business tax credits voted by the House. These credits are estimated to save between 100,000 and 200,000 barrels of oil aday by 1985.

The Senate committee already has turned down all of President Carter's major tax increase request which have been approved by the House - the gas guzzler, crude oil equalization and industrial use of oil and gas. It is focusing instead on tax incentives to increase production.

Yesterday the Senate panel voted to broaden the 10 per cent home insulation tax credit for homeowners who install solar heat to cover those who lease solar equipment.

And to the list of home equipment that qualifies for the insulation tax credit, it added energy, fluorescent lights and more efficient furnaces.

House Ways and Means Committee chairman Al Ullman (D-Ore.) said yesterday that if the Senate will approve some tax bill and send it to conference with the House, "I think we can work out a bill that preserves the basic policy decisions we made in the House".

That decision was to use taxes, credits and rebates to encourage conservation in the use of precious oil and natural gas and conversion to the use of more abundant coal. Critic contend Carter's program doesn't do enough to encourage production of more energy. The Finance Committee shares that view and is expected to vote tax concessions producing sizeable revenue losses to encourage more production of energy.