In a curtain-raiser to its upcoming fight over the oil windfall profits tax, the Senate broke a Sun Belt-Frost Bell impasse last night with a compromise over how to allocate $7 billin in fuel assistance to the poor over the next two fiscal years.

The compromise, approved 69 to 14 after it was reached in behind-the-scenes negotiations earlier in the day, would provide more money than originally proposed for heating subsidies in cold states but would retain substantial assistance for air-conditioning and other energy uses in other states.

Approval of the compromise, subject to modification when it is incorporated later in the oil profits tax, clears the way for Senate debate on the tax measure to start today. The proposed Senate bill would recapture about one-third of the profits oil companies are expected to reap from decontrol of oil prices -- about half what the House has approved and President Carter wants.

But the debate will not be limited to taxes. Sens. Lloyd M. Bentsen (D-Tex.) and Charles H. Percy (R-Ill.) yesterday said they will try to amend the oil bill to permit a tax exemption on savings account interest, starting with the first $100 of savings interest per person next year and rising to the first $500 by 1985.

At issue in the fuel allocation dispute is the formula for dispensing $7 billion in fiscal 1981 and 1982 in poor people's energy sudsidies, which would become part of the oil windfall profits tax bill if it is passed. It is a kind of energy-era pork-barrel fight between the Frost Belt and Sun Belt over how to skew a neutral-sounding formula to the advantage of one region over the other, ali in the name of shivering, or sweltering, poor people.

The colder states won the first round with a fuel assistance formula, heavily weighted toward them, that both houses have approved in a $1.6 billion appropriation for the current fiscal year.

The warmer states took the second round in the form of formulas more to their liking that were approved by the Senate Finance Committee and the Senate Labor and Human Resources Committee. These formulas would divide the $7 billion evenly according to two sub-formulas, one weighted toward the warm states, the other toward cold states.

But as the third round began on the Senate floor earlier this week, Sens. Edmund S. Muskie (D-Maine) and Rudy Boschwitz (R-Minn.) weighed in with an amendment that would vastly increase the coldest states' share of the money on grounds that their fuel needs and expenses are most critical.

This brought Bentsen to his feet, protesting that poor people can die of the heat as well as the cold, quoting a Dalls newspaper headline, "Heat Kills 11 More Here," to prove his point.

To make matters worse for Muskie, the Senate appeared ready yesterday to go along with a move by Sen. Bob Dole (R-Kan.) to set a minimum of $120 a year for individual household grants, which would amount to a boon for some Sun Belt states and, under Senate procedures, a parliamentary boobytrap for Muskie.

Senate Finance Committee Chairman Russell B. Long (D-La.) sat smiling as Muskie, his antagonist from many budget battles, fumed and threatened to adopt the old southern tactic of "extended aebate" (filibuster) to educate the Senate on the plight of the North.

In words familiar to the southern filibusterers of yore, Muskie berated those who would "ride roughshod" over a beleaguered minority, and observed, "I envy my southern colleagues who now serve by silence, whereas I have to serve by the unaccustomed tool of talk." Long just kept on smiling, and the Senate finally recessed on the issue Wednesday evening in hopes of reaching a compromise yesterday in behind-the-scenes negotiations.