House-Senate conferees agreed yesterday on a set of joint congressional budget targets for fiscal 1980, calling for a deficit of $23 billion - $6 billion less than President Carter had sought last January.

The compromise resolution, which still must be approved by both houses, essentially parallels the president's budget proposals, with an overall spending level of $532 billion and a sharp rise in defense outlays.

The reduction in the deficit came mostly as a result of different economic assumptions - primarily a higher inflation rate, which makes tax revenues higher. There were few changes in key programs.

Conference committee members averted difficult decisions on controversial issues by splitting the difference between House and Senate on key items without specifying what the increases or reductions would affect.

The purpose of the Budget resolution is to set broad overall targets for some 19 spending categories. How monies are allocated within those totals is decided by the Appropriations committees.

Yesterday's agreement followed 2 1/2 days of tedious debate in which little was accomplished until the final few hours. A Thursday night session broke up early after a temper outburst by Senate Chairman Edmund S. Muskie (D-Maine).

The measure now goes back to the two houses for final action next week. The lawmakers were supposed to have approved the resolution by May 15, but they missed their deadline after floor debate bogged down.

The targets agreed upon yesterday are only tentative limits, intended to serve as guides for the Appropriations committees. The two houses are scheduled to review the totals in September and set binding spending ceilings.

The action essentially was a victory for President Carter, who had admonished the lawmakers to hold down the size of the deficit and not cut his defense budget appreciably.

The compromise resolution decided on yesterday was closer, for the most part, to the Senate's version of the measure. The Senate had called for spending of $532.6 billion, while the House had approved $529.9 billion.

Here is what the conferees decided on key issues:

Defense: The conference panel voted to budget $124.2 billion for fiscal 1980 outlays and $136.6 billion in authority to commit funds for future spending - essentially the same as the Senate had approved.

The House had sought to slash new military spending authority by $3.1 billion, but the conferees balked. Carter sought $126 billion in defense outlays for next year - a jump of 3 percent, after inflation, from fiscal 1979.

Revenue Sharing: The panel rejected a House move to eliminate grants for states. The conferees restored $1.9 billion of the $2.3 billion the House had cut. Some $150 million of that amount will go for antirecession aid to cities.

Education and Jobs Programs: The conferees voted to budget $30.5 billion for this category, halfway between the Senate and House totals, but they did not specify how their action should affect specific programs.

The House had voted to approve half the reduction sought by President Carter in the "impact aid" for schools program, but added extra monies for higher education, aid to the handicapped and the Head Start program.

The Senate, on the other hand, had wanted to reduce Carter's request for the antirecession portion of the public-service jobs program. The conferees left these decisions to the House and Senate Appropriations committees.

Urban Initiative: Both houses approved Carter's revised, scaled-back aid-to-cities package, but without a modest portion Carter had sought that would have beefed up Housing and Urban Development Department grants.

Energy: The conferees agreed to a Senate move to slash funds for buildup of strategic petroleum reserves. The action, essentially a book-keeping function, was intended as a slap at the Energy Department.

The $23 billion deficit figure was also a compromise between the House and Senate versions. The House had approved a red-ink figure of $20.9 billion, while the Senate had called for a deficit of $29 billion.

Yesterday's resolution apparently dropped a series of specific House votes designed more as political statements than actual budget-cutting proposals.

These included a proposal by Rep. Joseph Fisher (D-Va.) to trim an extra half percentage-point from spending in all categories, and an overwhelming House vote to repeal the foreign tax credit for oil companies.

On most items, the House either accepted the Senate's recommendation for a spending category, or else virtually split the difference between its own specific proposals and those approved by the Senate. CAPTION: Picture, Rep. Robert N. Giaimo (D-Conn.) and Sen. Edmund S. Muskie (D-Maine) before start of yesterday's budget conference. By James K. W. Atherton - The Washington Post