In perhaps the most significant economic gamble in a generation, House-Senate conferees yesterday approved a $750 billion tax cut bill after cutting an $11.8 billion deal for the oil industry and dropping token amendments sought by Frost Belt members of Congress.

Senate leadrs had sought a final vote last night but were blocked by Sen. Edward M. Kennedy (D-Mass.), who forced postponement to Monday at 2 p.m., when Kennedy will get an anti-oil test vote calling on the Senate to send the measure back to conference committee. If, as expected, that fails, the Senate will immediatley vote on final passage. The bill is expected to be taken up by the House for final enactment on Tuesday.

In a 16-hour marathon session that ended at 8 a.m. yesterday, the conference committee significantly lowered the tax liability of the beneficiaries of estates exceeding $2 million; closed the "commodity straddle" tax loophole; increased the child care credit (but only after dropping a provision beneficial to the working poor); created a new deduction for charitable contributions; opened up individual retirement accounts to everyone; cut the capital gains tax rate for persons in the top imcome brackets retroactive to June 9; exempted income of up to $75,000 earned by U.S. citizens working abroad,moving up to a $95,000 exemption by 1986; raised to $125,000 the tax-free profits on a home sale by someone 55 or older, and gave all home sellers two years to reinvest profits in a new home to avoid taxation.

The bill is a major victory for the Reagan administration. When signed into las, it will mark completion of the basic foundation of the Republican economic strategy: deep cuts into domestic social programs combined with tax reductions largely benefiting corporation;s and the well-to-do. While not a direct part of the economic program, a third major factor entering into the equation is the administration's plan to raise defense spending to $1.5 trillion over the next five years.

At a briefing yesterday morning, Treasury Secretary Donald T. Regan declared, "We are willing to stand behind this bill and say we got what we want . . . This is President Reagan's tax program." Attempting to head off public expectations of immediate ecnomic improvement, Reagan said change will come slowly, comparing the shift to an ocean liner turning around. But he stood by the predictions in the administration's midyear economic review, which is far more optimistic than many private economic forecasters.

White House chief of Staff James A. Baker III contended that approval of the tax bill, prticularly in the nominally Democratic House, "confirmed the existence of a strong bipartisan coalition" behind the Reagan economic program. "There is a party realignment going on in this country," Baker said. "More and more persons in this country are self-identifying as Republicans."

The most significant parts of the tax bill -- 25 percent across-the-board rate cuts over 33 months, indexation of the tax system to the inflation rate and a new business depreciation schedule that effectively will cut corporate taxation nearly in half -- were not at issue in the conference committee.

Instead, the committee, working in a tiny room that forced lobbyists and most of the press to wait in the corridors, tackled and resolved the following issues over which the House and Senate had been in conflict:

In an unprecedented bidding war for the votes of oil-state House Democrats, the Reagan administration had proposed new exemptions from the oil profits tax, resulting in a $16.9 billion, five-year tax break that would rise to $46 billion by 1990. The Senate, normally more favorable to the oil industry than the House, buckled to the threat of liberal filibuster and gave the industry tax reductions of $6.6 billion through 1986 and $20 billion by 1990.

The conference committee split the difference at $11.8 billion over five years. Royalty owners will get a $2,500 credit in 1981, the equivalent of a $8,600 credit for 1982, 1984, and thereafter $10,900.Independently owned stripper wells would be completely exempted from the tax in 1983. The oil profits tax rate on all oil discovered after Jan. 1, 1979, would be phased down from 30 percent to 15 percent by 1986.

This compromise split the liberal camp in the Senate. Kennedy promptly threatened to delay the bill. He said in a statement: "I know that my colleagues wish to . . . leave the long hot summer of a Washington August, but I think we should stay in session until this issue is resolved." Kennedy reportedly was on Cape Cod, and succeeded in blocking action on the bill until Monday with the help of the Democratic leaders hwo remained in Washington over the weekend. A number of Republican senators complained that if Kennedy was serious, he should have stayed in town to fight his battles himself.

Sen. Howard M. Metzenbaum (D-Ohio), who had railed on the Senate floor Firday against the oil tax breaks, yesterday claimed the $11.8 billion "compromise" was a personal victory -- "I believe the fight I made has been worth it" -- and dropped filibuster threats.

In the one concession to opponents of the oil tax break, the conferees rejected a provision that would have frozen the depletion allowance at 22 percent.

The panel accepted a proposal, originally initiated by the Democrats, to reduce the top estate tx from 70 percent to 50 percent. This will apply only to estates exceeding $2 million and is part of a larger accepted plan to nearly eliminate the estate tax.Under present law, only about 140,00 of more than 2 million estates a year, the wealthiest 2.8 percent, are liable to a federal tax. The Reagan tax bill will lower this to 0.3 percent or about 7,000 estates. Over a five-year period, the estate changes will mean a total tax break of $15.6 billion, targeted almost entirely to the beneficiaries of very large estates.

The panel voted to create a new charitable deduction for taxpayers using the short form. The deduction would be up to $25 in 1982 and 1983, $75 in 1984, unlimited in 1985 and 1986, and would require re-enactment in 1987. Rep. Barber B. Conable Jr. (R-N.Y.) has advocated this provision as an added inducement to charitable giving, while liberal Democrats have complained that it amounts to an effort to get low- and moderate-income taxpayers, who make up the majority of short-form users, to help finance through private contributions programs that fell victim to the Reagan budget-cutting effort.

In a direct slap at northeastern and midwestern members of Congress, the panel deleted two relatively minor tax breaks, a credit for woodburning stoves that would have cost $625 million over six years nad a one-year home heating credit that would have cost just over $500 million.

The conference committee agreed to a House provision allowing U.S. citizens working abroad to exclude up to $75,000 of their income from taxation here, rising in $5,000 steps to $95,000 by 1986. In addition, those working overseas could take unlimited exclusion for housing costs in excess of $6,100.

The panel also approved an increase in the child care credit, raising the maximum from $400 to $720 for a working couple with one child and to $1,440 for a couple with two or more children. This would drop to a ceiling of $480 and $960 respectively when the couple's income reached $30,000 or more. The committe dropped, however, a section making the credit refundable in the case of working poor parents who have no tax liablity -- in other words, a direct payment to the couple from the government.

Conferees stripped from the bill a unrelated provision aimed at allowing employes to take control of Continental Airlines. The amendment was made last week by Sen. Dennis DeConcini, D-Ariz., whose brother-in-law is a pilot for the airline.

The conferees rejected a House proposal to make the holding period for capital gains six months instead of a year.