Mayor Marion Barry's key aides said yesterday that his administration was not surprised to find a potential $60 million gap in a budget they previously claimed was balanced, and promised "a series of management steps" -- including possible layoffs -- to close the gap by Sept. 30, when the fiscal year ends.

On Thursday, Barry told members of the City Council at a closed-door briefing that departmental overspending and unexpected pension and welfare costs could create a gap as large as $59.9 million in the city's $1.4 billion operating budget for the current year.

City Administrator Elijah B. Rogers maintained yesterday that the gap could not be considered real until the end of the fiscal year.

"We do not have a deficit," Rogers said. "We're going to take a series of corrective steps."

While not specifying what steps city officials were considering, Rogers would not rule out the possibility of more layoffs, setting the stage for a sharp and potentially bitter confrontation with city employe unions when collective bargaining over wages begins later this year.

"Our last resort will be layoffs," Rogers said. "We will cross that bridge when we come to it."

The disclosure of the potential budget gap marked the second time that an apparently balanced city budget was belatedly found to be unbalanced.

Last year, Barry aides discovered a budget gap at first projected to be about $27 million, but later estimated as high as nearly $180 million. To avert the deficit, Barry reduced the work force by about 1,100 workers, held down pay raises and implemented a package of tax and user-fee increases.

Nevertheless, the city wound up with a $105 million deficit for that fiscal year, which ballooned the deficit accumulated over several years to $388 million. According to persons who attended Thursday's meeting, Barry said that if the current year ends with a fiscal gap, the deficit simply may be rolled over into the next fiscal year, adding to the $388 million figure.

The potential deficit is actually lower than might be expected because income increases and rises in property-tax assessments have yeilded revenues 20 percent higher than projected earlier by city budget planners.

City officials blamed the Department of Human Services, the District's largest agency, for much of the current overspending. Payments for Medicaid and the Aid to Families With Dependent Children programs are costing substantially more than expected.

Rogers said yesterday that he had maintained all along that the city's public assistance programs would cause a budget problem during this year, which will only worsen next year as the federal government prepares to trim its contribution to such programs.

But several members of the City Council were swift to criticize Barry for not recognizing soon enough that DHS public assistance programs were severely underfunded, forcing the department to continue to overspend.

"It's a persistent problem," said council member Betty Ann Kane (D-At Large). "The continued overspending is in many of the same areas as last year. And, if those are truly the areas where the overspending is projected, it's hard to cut back on. You can't just throw people off welfare."

In addition to the $60 million potential deficit, Barry also told the council members of a cash shortage, also $60 million, this summer -- after the city refunds $40 million collected through a tax on professionals that was later declared illegal and exhausts the money collected from spring property and income-tax payments.

Philip M. Dearborn, Barry's newly hired financial adviser, said the coming summer drought in revenues could be considered typical in some respects. "Summer is a low point for receipts," he said. "This year is likely to be deep."

With little or no money in the city treasury this June, city officials will likely to have to go the U.S. Treasury Department for a loan, Dearborn and Rogers said.

There is no limit on how much money the city can borrow from the Treasury Department, but the city still owes the Treasury $40 million from previous, unpaid loans. Rogers said yesterday that any more money borrowed would be paid back by the end of the fiscal year.

Yesterday evening, after declining throughout the day to comment on the deficit, Barry issued a press release, saying he had "moved to insure" that the budget remained balanced.

The press release said Barry directed top officials to "take corrective measures to insure that there will not be a deficit by the end of this fiscal year." It did not say what those measures would be.