The House Budget Committee approved a fiscal 1979 budget that is $6.1 billion below President Carter's latest proposal and $8.3 billion less than the tentative 1979 budget Congress adopted last spring.

The action came just a week after the Carter administration urged Congress to trim $5 billion from the President's latest budget proposal in order to help fight inflation.

The House Budget Committee proposal, which will go to full House later this month, leaves room for a $19.4 billion tax cut next year, bigger than the $16 billion tax cut approved by the House Ways and Means Committee last week.

The sharp trim in the spending level approved by the committee - from the $498.8 billion adopted tentatively last spring to $490.5 billion - does not represent major program cuts. Instead it relects re-estimates of spending for next year as well as cuts in appropriations bills made by Congress this summer.

If the House committee budget is adopted by Congress, the deficit would be $43.7 billion next year. In the current fiscal year, which ends Sept. 30, the deficit will be about $51 billion.

Rep. Robert N. Giaimo (D-Conn.), chairman of the committee, noted that if Congress adopts a smaller tax cut than allowed in the budget resolution, the deficit could shrink to near $40 billion.

Next week the Senate Budget Committee will begin work on its version of the fiscal 1979 budget. Fiscal starts Oct. 1.

By Sept. 15, the House and Senate must agree on a joint budget that sets overall spending ceilings and revenue floors that can be changed only by special vote of Congress. The spring budget resolution is a guide to taxing and spending actions, but the ceilings are not binding.

The House committee rejected a Republican move to permit a $28 billion tax cut in calender year 1979 ($20 billion of which would fall in fiscal 1979) and a move by conservative Democrat Otis Pike of New York to allow for a tax cut of only $9.3 billion.

The Carter administration, in its new-found zeal to trim spending, has also promised it will shoot for much tighter budgets in fiscal 1980 and fiscal 1981.