A senior White House official said yesterday that it would be difficult to get President Reagan to accept an oil import tax being suggested by Senate Republicans to reduce the budget deficit because it would "certainly" violate Reagan's pledge not to raise taxes.

But the official said Reagan will not make a decision until he gets a chance to examine a larger deficit-reduction package that is expected to include the oil tax. Reagan is scheduled to meet with congressional leaders on the package next week, he said.

It would take "a big . . . horse pill to get him to swallow this," the senior official said of the oil import fee. Reagan has opposed such taxes in the past and yesterday told reporters, "I'm not for any taxes."

But the official said there is serious concern in the administration that collapse of the House-Senate budget conference could seriously impair the prospects this autumn for Reagan's proposal to overhaul the tax laws.

Without a budget resolution and the spending cuts it would include, sharp battles can be expected over a continuing resolution to fund the government in the new fiscal year that begins Oct. 1, the official said. This would lead to a politically "messy September and October," exactly the period in which Reagan hopes Congress will vote on his tax plan. The result could be an effort by Congress to use the tax plan to raise revenues.

"We don't want that," he said.

The senior official, who asked that these comments not be attributed to him by name, said in an interview that the oil import fee backed by the Senate Budget Committee conferees and Senate Majority Leader Robert J. Dole (R-Kan.) would run counter to Reagan's pledge not to raise taxes. Reagan made the vow in his 1984 reelection campaign and has repeated it often since.

"That's the whole problem with us," the official said, suggesting that it would not be easy for Reagan to abandon his position on taxes.

The senior official said there are now three schools of thought about the budget negotiations. One is that all sides are simply maneuvering to avoid the blame if the talks collapse and Congress begins its August recess without voting to reduce the deficit.

"Everyone wants to make sure they're not underneath this thing when it collapses," said another White House official.

The second scenario, said the first official, is that Reagan will accept a budget resolution -- possibly with tax increases -- to settle the issue now and leave the autumn open for his push to revise the tax code.

The third scenario, he said, is that Reagan and Congress agree to a scaled-down budget resolution along the lines of what the Democratic-controlled House has already approved. This is the "chicken school" of thought, he said, "But you know, maybe it's chicken if you can't have steak."

Long an opponent of tax increases, Reagan won a major tax cut in 1981. But in his first term he later accepted four major tax increases that reclaimed about one-third the revenues lost in the initial tax cut. In bargaining with Congress, Reagan has often held out against tax increases until the last minute, then accepted them.

The tax issue has been one of the philosophical touchstones of Reagan's presidency. White House chief of staff Donald T. Regan predicted in an interview yesterday that the president's recent cancer surgery would make him less willing to compromise his main goals during the remainder of his second term. "I think if anything it has reinforced Reagan wanting to be Reagan," the chief of staff said.

Doctors have said Reagan has a better than 50 percent chance to survive the next five years with no recurrence of the disease. But the cancer surgery has led many White House officials to speculate privately that Reagan will nonetheless feel a sense of urgency in the final years of his presidency, not only because of the political calendar but also because of his health.

These officials noted that the assassination attempt that almost took Reagan's life in 1981 had a similar effect. Shortly after the shooting, he met with the late Cardinal Terence Cooke, the Roman Catholic archbishop of New York. "The hand of God was upon you," Cooke said to Reagan.

"I know," Reagan replied. "And whatever time He's left for me is His."

Yesterday, the senior White House official said Reagan's thinking is "still in formation" in the area of relations with the Soviet Union as he prepares for the September meeting with Foreign Minister Eduard Shevardnadze and the November summit with Soviet leader Mikhail Gorbachev.

"I think he plans to do a lot of thinking about that over a period of time, watching what the Soviets do, how they act, are there any signals as to what they're going to do?" he said. "He has to think that one through very carefully."

Commenting on widespread news accounts of his highly visible position at the White House during the president's operation and convalescence, chief of staff Regan said yesterday that the surgery simply highlighted the functions he was already performing. "That's the whole thing. That's what I have concluded," he said.