A sharply divided Reagan administration is weighing a proposal to prop up marginal oil producers in the United States by doubling or tripling the 50-cent-a-barrel excise tax on imported oil and using the proceeds to buy domestic oil for the Strategic Petroleum Reserve.

The proposal has generated some interest among oil-state members of Congress and administration officials concerned about the impact of falling oil prices on the domestic industry. It is unclear, however, how the tax increase would be received at the White House, which has opposed recent efforts to impose new fees on imported oil and affirmed this week that it has no intention of interfering with the world oil market.

Two months ago, President Reagan said he might be willing to accept new taxes on oil imports as part of an effort to restructure the tax code, but he withdrew that tentative support last month, saying he was convinced that the fee "would have a bad effect on the economy."

Supporters of the idea defend the excise tax as a "user fee" that would bolster the nation's defenses against overreliance on imported oil. But the argument has its skeptics, including high-level officials at the Energy Department who have been casting about for ways to protect the U.S. oil industry.

"What's the difference between an excise tax and an import tax?" said a department spokesman. "The position of top officials in this office is that we would not favor such an approach."

The disagreement highlights the administration's dilemma in the face of four months of steadily falling oil prices, which White House officials have credited in large part to the administration's free-market policies.

The initial euphoria over the economic boom that results from cheaper energy has given way to concern over the long-term impact on domestic producers and the national security implications of losing a significant segment of U.S. production.

The issue also has created some divisions within the administration. Vice President Bush and Energy Secretary John S. Herrington have spoken up publicly for the domestic oil industry, and Interior Secretary Donald Hodel is privately sympathetic. White House chief of staff Donald T. Regan and Treasury Secretary James A. Baker III are said to be adamant about letting the market take its course.

The sagging oil market has implications for the federal budget, as well. The administration has estimated $4.6 billion in receipts this fiscal year from the windfall profits tax on oil, which for all practical purposes has been repealed by plummeting prices. For fiscal 1987, the Interior Department has projected revenues of more than $6.3 billion from bonuses, rents and royalties on federal oil and gas leases.

For the moment, however, attention has focused on the "stripper" wells, which typically produce less than 10 barrels of oil a day, and other marginal wells with high costs and low production. More than 450,000 such wells were operating at the beginning of the year, mostly in Texas and California, producing from 12 to 14 percent of the nation's oil supply.

Thousands of stripper wells have been shut down in recent weeks. Energy analysts predict that thousands more will follow if oil prices remain at current levels, deepening the financial crunch in oil states and increasing the nation's dependence on imported oil.

A special interagency task force has been considering continued purchases for the Strategic Petroleum Reserve as a way of providing more insurance in case of market disruptions, and congressional sources said there is interest on Capitol Hill in structuring the purchases to help keep marginal wells pumping.

Administration officials participating in the task force said its work has not progressed beyond the question of how much oil the nation needs in reserve. "After you decide that, then you give attention to where you're going to get the oil and how you're going to pay for it," one official said.

But congressional and other sources said the task force is considering a proposal to finance purchases through an increase in the existing 50-cent-per-barrel excise tax on imported oil, to $1 or even $1.50, which would provide up to $4 million a day to buy oil for the reserve.

Because the revenues would be used only to fill the reserve, the proposal differs significantly from the much larger oil-import fee suggested earlier this year by members of the Senate Finance Committee who were seeking ways to replace revenue that would be lost under income-tax revisions sought by the administration.

The proposal would require congressional action, both to authorize the higher excise tax and to direct the Energy Department to purchase oil from domestic producers rather than from Mexico, which is the current source of oil for the reserve.

An aide to Sen. Lloyd Bentsen (D-Tex.) said that the proposal will be regarded warily, not just by the White House but by representatives of oil-dependent states.

"It's going to be a subsidy, no matter how you cast it," he said. "But you have to approach it from the standpoint of national security and economic stability."

The proposal has aroused interest among some conservative economists, however, including Milton R. Copulos, a Heritage Foundation energy analyst.

"The argument is being made with some validity that the Strategic Petroleum Reserve is an insurance policy against imported oil, so it can be argued that you could have a user fee to finance the SPR fill," Copulos said. "User fees are consistent with the free-market philosophy."

Copulos also argued that no less a free-market authority than Adam Smith approved of trade tariffs if they were evenly applied. Domestic producers, Copulos said, already pay an equivalent tax through the windfall profits tax. "Even if it's not collected, the cost of paperwork is a buck a barrel," he said. "One might argue that a dollar a barrel is equivalent to an excise tax."

In Texas, oil economists greeted the idea with less enthusiasm. "It would be some measure of help to protect stripper production, but it is nowhere consistent with the degree of the problem we face," said William Fisher of the University of Texas. "It's a relatively small step in the right direction."