Murray L. Weidenbaum, chairman of the president's Council of Economic Advisers, said yesterday the administration will be able to keep the federal deficit under $100 billion in each of the next two fiscal years, and this year as well.

Administration forecasters have said that without further spending cuts or tax increases the deficit will exceed $100 billion this year and $150 billion in each of the next two.

Weidenbaum said further spending cuts were still possible this fiscal year, which began Oct. 1. He said these would keep the deficit under $100 million.

For fiscal 1983 and 1984, he said the deficits would be progressively smaller than this year's. This progression could theoretically be achieved, he said, merely with "cuts on the spending side," and not by tax increases. But he carefully avoided ruling out tax increases, nevertheless.

The tax increase question has been much debated within the administration. David A. Stockman, the director of the Office of Management and Budget, has reportedly been arguing for some increases to help reduce future deficits.

Treasury Secretary Donald T. Regan has reportedly led those arguing against such devices, except as a last resort. But sources said yesterday that Regan now seems willing to contemplate significant tax increases for 1983 and 1984, provided that these do not involve postponing the personal income tax cuts enacted last summer and due to take effect in July, 1982, and July, 1983. Regan also opposes any major change in the business tax cut enacted this year, sources said.

Weidenbaum warned at a breakfast meeting that even if deficits in the next three years are not in "triple digits," the era of large deficits will last well past 1984, the year the administration had originally planned a balanced budget.

The president's economist would not comment on the reported split among Reagan advisers on tax increases, nor indicate on which side he lines up.

He did hint, however, that if a tax on natural gas were to be considered in connection with a proposal to speed up deregulation of natural gas prices, he would favor an excise tax, rather than a windfall profits tax, which other administration officals have recommended. He estimated that either tax, windfall or excise, could be structured to yield $10 billion to $20 billion annually.

The forthcoming federal deficits produced a political flare-up last week when Weidenbaum and fellow economic council member William A. Niskanen said publicly that the importance of deficits had been exaggerated.

Niskanen took the bolder position, arguing contrary to traditional Republican rhetoric that "there is no direct or indirect connection between deficits and inflation." He added that it was better to tolerate the deficits than to reinflate the economy or to raise taxes in order to get rid of them.

But Weidenbaum stressed yesterday that the administration believes that "deficits are important," and disputed Niskanen's analysis, especially his assertion that government deficit-financing does not crowd private borrowers out of the money market.

Niskanen had "presented some preliminary findings of on-going academic research. He presented only three scatter diagrams without a formal paper. It wasn't intended to be a statement of administration policy, and I assure you it wasn't," Weidenbaum said.

"It is clear to me that budget deficits and government financing of them competes with private financing for available investment and savings funds," he said. "To the extent that private needs are crowded out, we get a lower rate of economic growth--and that is the single most important result of deficits and that's why it's so important to get those deficits down."

Nonetheless, Weidenbaum endorsed another controversial statement made by Niskanen, to the effect that eliminating deficits and achieving a budget balance in fiscal 1984 had not been a key point in the Reagan campaign last year.

"If you look at the Feb. 18, 1981, white paper on the Reagan economic program , you will find that the central commitments were to slow down the growth of government, to slow down the growth of spending, to reduce the percentage of national income going to the treasury, to reduce taxes, to reduce the growth of regulations, and to follow a policy of monetary restraint," Weidenbaum said.

"These were the central features and they remain so. And we've made progress in all . We did forecast a balanced budget, making certain economic assumptions, but that was not presented as one of the fundamental objectives on a par with reducing taxes, spending and regulations."