The Senate last night approved a tax to raise $178 billion from the decontrol of oil prices over the next decade -- with a tax break for small savers thrown in as a political bonus.

The 74-to-24 vote on the tax, a scaled-down version of a tougher levy voted earlier by the House, followed a month of debate that was topped off by a three-day filibuster last week over the size of the tax and whether it should be applied to newly discovered oil.

The measure now goes to a House Senate conference, where the Carter administration is expected to push hard to get back as much as it can of the nearly $100 billion in anticipated revenue that the Senate lopped off the $277 billion House bill.

Although Senate leaders ave said they want to get a complete tax package, along with Chrysler Corp. relief legislation, to President Carter by Christmas, it appeared last night that final action could go over into early 1980.

The first conference meeting is not planned until Wednesday, only two days before Congress hopes to quit for te holidays. Senate Finance Committee Chairman Russell B. Long (D-La.) said he thought final action was possible this week, but House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) indicated he was more interested in a strong bill than speedy action.

Regardless of the final size of the tax, it will be the biggest levy on a single industry in American history -- an attempt to recover for the government some of the enormous profits expected to flow to oil producers from Carter's gradual lifting of controls on crude oil prices.

Last night, most of the "no" votes came from Republicans who complained that the tax was too stringent, despite administration assertions that the Senate version is too weak.

All Washington-area senators voted for the oil tax bill on final passage.

The small-savers proposal, which the Senate tacked onto the oil bill, would exempt the first $200 of combined savings account interest and dividends -- or $400 on a joint return -- from federal taxation. Currently only $100 of an individual's dividend income, or $200 on a joint return, is exempt.

The small-savers proposal had nearly 80 cosponsors and passed by 94 to 4, an indication of its appeal on the eve of an election year.

The only outright opposition came from Senate Budget Committee Chairman Edmund S. Muskie (D-Maine), who disputed a claim by the proposal's chief sponsor, Sen. Lloyd M. Bentsen (D-Tex.), that it would encourage saving and thus produce capital for business expansion. Basically, said Muskie, it would simply give a tax break to people who are already saving.

Acknowledging that his words wouldn't be heeded, Muskie said there were four things wrong with the proposal: "It won't work. It isn't fair. It isn't necessary. An . . . it will leave us $27 billion less to work with."

Bentsen argued that although the exemption would cost the Treasury an estimated $27 billion over the next decade, it would pay for itself in terms of capital expansion and national productivity. Responded Muskie, "This is petty gilt polishing masquerading as populism."

Although the House bill doesn't include a comparable provision, Bentsen said he thinks the amendment's chances in Congress are "excellent" in light of its strong showing in the Senate.

Earlier, the Senate finally, on its fourth try, had invoked cloture to limit debate and amendments and thereby speed up action on the measure. This weeded out a number of nongermane amendments, including proposals to let tax rates rise if oil prices soar above the bill's projections, tie favorable rates on selected types of oil to energy reinvestment by producers, and impose a 50-cent-a-gallon gasoline tax. The gasoline tax proposal similar to one under review by the administration, died without mention.

The 84-to-14 vote to impose cloture came only after a compromise Friday that set the ultimate size of the tax at $178 billion over the next decade. This was about $40 billion more than the Senate Finance Committee proposed but still far short of the House version, which anticipates $277 billion by 1990, or nearly as much as the administration wanted.

The gap between the two bills arises largely from the fact that the Senate version provides generous exemptions for independent producers and lower tax rates for certain categories of oil produced largely by major oil companies. These include newly discovered oil, heavy oil and oil produced by expensive "tertiary" recovery methods. The House's heavier tax on newly discovered oil accounts for the single biggest difference.

One of the major struggles in the conference is expected to come over whether independent producers or the major oil companies bear the brunt of any increase beyond what the Senate proposed.

Another major difference, although it does not figure in the 1980-1990 revenue projection, is that the House tax would continue indefinitely while the Senate would be phased out when the total revenue yield reached $214 billion. This would happen during the mid-to-late 1990s under current revenue estimates. Higher-than-anticipated oil prices would mean a faster phase-out.

The Senate version would tax only about one-third of the estimated revenue from decontrol after other tax liabilities are subtracted, while the House bill would take about half of it.

The revenue estimates of $178 billion for the Senate bill and $277 billion for the House version are based on oil price assumptions made before the latest round of OPEC increases and could be low by as much as $100 billion over the next decade, according to some congressional tax sources.

But with soaring prices, oil company profits would rise even more than tax revenues under the Senate bill because the companies would get twice as much as the government from any price increase. To get more of the money for the government, Sen. Henry M. Jackson (D.-Wash.) proposed to let the secretary of the Treasury adjust the specific tax rates in the bill to conform to actual price increases if the price per barrel exceeds $30, as it is expected to do next year.

Jackson's proposal was attacked by Sen. Bob Dole (R.-Kan.) as a "lastditch effort to wreck the [oil] industry," and by other oil state senators as an invitation to confiscatory taxation by a presidential appointee. s

It finally died without a vote when it was held to violate the germaneness (relevancy) rule that cloture imposed.

Buried with it was another Jackson proposal to let oil companies qualify for lower rates for newly discovered, heavy and tertiary oil only if they actually plowed their profits from decontrol back into energy development. Dole, attacking this proposal as well, called it a "plow-under" amendment.

Later, Jackson charged that the Senate bill fails to protect the United States from OPEC price increases and actually invites domestic producers to encourage such increases because higher prices would mean a quicker phase-out of the levy.

"We are leaving ourselves bare to these price thieves," said Jackson, who asserted that the tax bill is so deficient that Congress will probably have to enact another oil tax bill next year.