The Senate yesterday rejected the recommendation of its Budget Committee and boosted spending authority for low- and middle-income housing by $6.2 billion in its 1978 budget.

The Senate also added $500 million in spending authority for community development and increased spending for veterans by $400 million.

While some liberals have recently bemoaned the Carter administration's "fixation" with balancing the budget by 1981 because it causes social programs to suffer, yesterday's action found the Senate and the administration in agreement on how much ought to be spent for housing and community development.

The Budget Committee had cut $6.2 billion from Carter's $32.8 billion request for assisted housing and $500 million from its $4 billion request for community development.

Neither of yesterday's increases in spending authority would result in a large increase in outlays in the federal spending year which begins Oct. 1, but they would permit the Department of Housing and Urban Development to make commitments to spend the money three, four or five years later.

The Budget Committee estimated that the two amendments would boost spending by only $40 million in 1973, with most of the remaining $6.7 billion in spending authority showing up as outlays in 1979 and beyond.

The boost in veterans' benefits widened the $63.2 billion deficit recommended by the committee to $63.6 billion.

The House, which last week bogged down in its attempt to write a 1978 budget, tries again today. Last week liberals, angered over a big increase in defense spending at what they claim is the expense of social programs, joined conservatives distraught over a big deficit to over-whelmingly vote to send the House version back to committee.

House Budget Committee Chairman Robert N. Giaimo (D-Conn.) worked out a compromise budget which adds $300 million to defense spending - $2 billion less than the President and the Armed Services Committee want - in an attempt to mollify both factions. Another rancorous session is expected today, although the House leadership thinks it can approve a tentative budget resolution on a close vote.

The House and Senate are supposed to agree on a joint budget target by May 15. Until both houses have approved a tentative 1978 budget, neither can consider any type of spending bill for fiscal 1978.

Congress is in the second year of a [WORD ILLEGIBLE] budget process designed to give the same ability to deal with overall [WORD ILLEGIBLE] that the President has. While the President recommends a federal budget each year, only Congress has the authority to tax and authorize spending.

While President Carter recommends a budget deficit of $57.9 billion next year - compared with the Senate's $63.6 billion and the House committee's $66.3 billion - much of the difference comes about because of different economic assumptions and not because Congress is proposing to spend substantially more than Carter.

The Senate, for example, plans out-lays of $459.2 billion next year, smaller than the President's $461.7 billion.

The administration had lobbied for the restoration of the $6.2 billion for assisted housing and the $500 million in community development cut by the Budget Committee. HUD Secretary Patricia Roberts Harris is committed to $500 million of "urban development action grants" designed to give one-shot support to projects in specially needy areas.

The boost in spending authority for low-income housing would increase by more than 50,000 the number of housing units HUD can put under contract next year. Both increases were proposed by William Proxmire (D-Wis.) and Edward W. Brooke (R-Mass.) chairman and ranking minority member of the Senate Banking Committee, which has jurisdiction over both programs.

Budget Committee Chairman Edmund S. Muskie (D-Maine) unsuccessfully fought all attempts to boost the budget spending levels.

"We cannot reduce the deficit merely by eliminating obvious and frivolous programs. We're going to have to reduce meritorious programs . . . I've got to say no over and over again to worthwhile budget initiatives to preserve restraint."