The Carter administration yesterday released revised estimates of the budget for fiscal 1978 (ending Sept. 30, 1978), trimming the deficit by $3 billion from mid-summer expectations to $58.5 billion.

Acting Budget Director James T. McIntyre Jr. said the new figures "make good news" for the financial and investment community because the numbers are "more realistic" than before, providing a fairly accurate estimate of the government's debt management needs.

Though the deficit has been cut back from the $61.5 billion figure projected last summer, it is almost $1 billion higher than the original budget guess last January, and $13.5 billion larger than the $45 billion red-ink total for fiscal 1977.

But McIntyre said the administration is not giving up its determination to reach a balanced budget in fiscal 1981. The target for fiscal 1979, he said, is a deficit "in the neighborhood of $40 billion.

On the other hand, McIntyre made clear that the 1979 target is not set in concrete. The revised figures for fiscal 1978 and the rough calculation for fiscal 1978 and the rough calculation for fiscal 1979 are still based on economic assumptions of early 1977, which anticipated a strouger economy than is being experienced.

President Carter and his aides recently stressed the probability of a major tax cut for calendar 1978, which could drastically affect actual results and budget policy.

McIntyre said no formal changes would be made in the economic assumptions until the results of the fourth-quarter gross national product are known.

Revised expenditures for fiscal 1978, as published yesterday, would be $459.8 billion, with receipts at $401.4 billion. The $3 billion reduction in the deficit, compared with mid-year, is all on the expenditure side.

McIntyre said the spending "shortfall" is now estimated at $11.1 billion for fiscal 1978, fractionally lower than the $11.5 billion gap between estimated and actual spending in fiscal 1977. About $4 billion of the shortfall is in military programs, with the rest widely scattered.

McIntyre said that appropriate congressional committees had agreed to a postponement of the "current services" estimates - which show how the budget would looks if current programs were merely extended - until the regular budget is issued in January.

He refused to comment on questions relating to the prospect that he would succeed Bert Lance as director of the Office of Management, and Budget.