The Reagan administration appears ready to try to break its commitments with key congressional members -- Republicans as well as Democrats, and particularly from the Frost Belt -- in an effort to trim the budget further when Congress returns from its summer recess, sources said yesterday.

Reagan officials hope to use the appropriations process to cut perhaps as much as $15 billion more from the budget for fiscal 1982.

Among the programs reportedly under serious consideration for new reductions:

* The Youth Training and Employment Act. The administration had sought to cut this altogether, but, with bipartisan support, Congress kept it alive at just over $500 million in 1982.

* Low-income energy assistance. The administration had sought to reduce this funding to $1.4 billion and fold the program into a block grant. Congress, however, maintained funding at $1.87 billion and modified the block grant proposal.

* Subsidized housing. The administration is concerned that congressional plans to encourage the use of this money for renovation of existing units, instead of new housing, will result in faster spending, thus deepening the deficit.

The food-stamp program is subject to further revision because cutbacks in welfare and housing allowances will make those beneficiaries eligible for more food stamps, and the spending targets will be inadequate to meet their needs.

After forcing major cuts through Congress in the budget reconciliation bill passed last month, Budget Director David A. Stockman has now turned his attention to the appropriations bills, which will determine actual spending levels for 1982, in an effort to hold next year's deficit to the $42.5 billion forecast by the White House.

Although still in exploratory stages, cuts are being considered in a network of programs that some members of Congress felt were protected by commitments made during the White House negotiations for support of its budget bill.

"This is pretty dangerous ground to go on," Rep. Frank Horton (N.Y.), a leading member of the group of Frost Belt Republicans known as Gypsy Moths, said. "These things were worked out and we had a pretty firm commitment on them." The chairman of the Gypsy Moth Republicans, Carl D. Purcell (Mich.), said, "I think our group would take the position of hold the line. These were the commitments...tough, hard-line agreements."

Congress has all along promised more spending cuts than those included in the reconciliation process, but these were never spelled out in detail. Some were to come from administrative savings -- such as cutting waste, fraud and abuse -- and some through cuts in appropriations not included in reconciliation.

A budget spokesman identified five areas where additional spending threatens the administration's deficit target:

* Higher interest rates, which could add $4 billion or more to 1982 spending.

* Social Security spending, where the administration assumed $3.8 billion savings from changes that Congress appears unlikely to pass.

* The farm bill, in which spending is likely to overshoot the Office of Management and Budget targets.

* Entitlement spending, which OMB says was $2 billion higher after reconciliation than the president wanted.

* Appropriations bills already through the House which OMB says are $2.7 billion higher than requested.

One strategy the administration is preparing is to press for funding of programs at levels proposed last March 10, when the budget cuts were first outlined in detail. About $3.5 billion in 1982 outlays could be saved if appropriations committees return to the spending levels requested by the president for those items capped in reconciliation, a budget spokesman said.

Cuts beyond the March 10 level are likely only if the president decides to trim defense spending, sources said. This is essential, many experts believe, if the administration is to make credible its forecast of a $42.5 billion deficit next year.

But it is likely to be difficult even to hold to the March 10 levels. The March spending proposals were significantly modified during negotiations over the reconciliation process.. These talks centered on two key groups of House members, the Gypsy Moths -- about 25 Republicans from the Northeast and Midwest -- and the Boll Weevils -- 47 conservative Democrats, almost all from the South.