Office of Management and Budget Director David Stockman conceded yesterday that the budget deficit could soar to as much as $100 billion by 1984--the year when President Reagan has promised to balance the budget.

Meanwhile, the Treasury announced borrowings of $8.75 billion for November, at the upper end of the range expected by the market.

Speaking to reporters after a congressional hearing, Stockman said "there are enormous upward pressures" on the budget that could threaten the $43.1 billion deficit target for fiscal 1982 and the balanced budget by 1984. However, he stressed that the administration has a $115 billion, three-year plan of budget cuts and tax increases that could bring a balance by 1984.

Many outsiders, including the Congressional Budget Office, have predicted that much larger savings will be needed to come close to Reagan's target. The last administration estimate showed that, without further cuts, the 1984 deficit will total $58.8 billion. Stockman yesterday agreed that the comparable CBO figure of $100 billion was "not out of the ball park."

He called for "some very tough and very serious action" in Congress to bring down the deficit and warned that "we will insist that Congress takes some action one way or another this fall."

But it is not clear how Reagan can "insist." He has had little success in Congress with his latest round of budget proposals. He has still to decide the details of proposed cuts in entitlement programs, which a budget spokesman yesterday said should be ready to go to Capitol Hill next week.

In the fiscal year just ended, the deficit totaled $57.9 billion, the Treasury and the OMB announced jointly yesterday. This is down marginally from the 1980 deficit of $59.5 billion, and up slightly from the July official estimate of $55.6 billion. Revenues were down by about $3 billion from the July estimate for a combination of reasons which may have been linked to a slowing economy, Treasury Undersecretary Beryl Sprinkel said yesterday.

Sprinkel told reporters when announcing the new Treasury refinancing that the Treasury has decided to continue selling long-term bonds on a regular basis. Some analysts have suggested that the Treasury should show its confidence in its forecasts that inflation will slow by refusing to sell long-term government bonds at present high interest rates.

However, the Treasury had rejected this argument in favor of continuing to sell securities across the possible spectrum, Sprinkel said.

The "brutal fact" is that "we have a massive amount of financing" to be done in the months ahead, he said, implying that it is necessary to sell, however possible. The Treasury estimates its net borrowing needs for the current quarter at $35.75 billion, assuming a cash balance of $12 billion at the end of the quarter, Sprinkel said.

This includes about $5 billion of additional financing in this quarter because there is a holiday weekend at the start of January. The cash balance at the end of September was $18.7 billion. Sprinkel said that present estimates of borrowing needs in the first quarter of 1982 are $29 billion to $32 billion, assuming a cash balance of $10 billion at the end of March.

After next week's sales, the Treasury will have raised approximately $16.75 billion in marketable borrowing towards the $35.75 billion quarterly total, the department said.

Yesterday it announced the sale of $8.75 billion of securities to refund $5 billion of publicly held coupon debt maturing on Nov. 15, and to raise $3.75 billion net new cash.

Three securities were announced yesterday:

* $4.5 billion of 3-year notes, maturing on Nov. 15, 1984, and to be auctioned on a yield basis next Monday at 2.30 pm. Minimum denomination: $5,000.

* $2.25 billion of 10-year notes, maturing Nov. 15, 1991, and to be auctioned on a yield basis next Wednesday. Minimum denomination: $1,000.

* $2 billion of 30-year bonds, maturing Nov. 15, 2011, callable beginning Nov. 15, 2006, and to be auctioned on a yield basis next Thursday. Minimum denomination: $1,000.

On each of the three securities, the Treasury will accept noncompetitive tenders of up to $1 million.