The real battle of the budget began shaping up yesterday as the House Appropriations Committee reported out three more money bills for next year.

One of the three would freeze the pay of the highest-paid 30,000 employes in the legislative, executive and indicial branches -- including members of Congress -- who earn more than $50,112.50 a year. If the rider is approved, 7,000 other top civil servants in the Senior Executive Service who are entitled under law to bonuses up to $20,000 a year would be limited to $52,750 in pay and bonuses combined.

This pay freeze, denying affected employes the cost-of-living increases most other government workers will probably get Oct. 1, was tacked onto a bill that will give the country another billion-dollar Congress. As sent to the House, the bill provides only $970 million. But that does not include Senate expenses. Each branch votes its own funds and traditionally does not touch the other's. Senate add-ons will push the total over $1 billion.

The committee also approved an agriculture money bill providing $21.9 billion in new spending authority plus $13 billion in loans and transfers. But the biggest item in the farm bill has to do with eating food rather than growing it. It is the food stamp program -- a subsidy for the poor which began as a way of disposing of surplus farm commodities.

The budget emphasis so far this year -- though it may shift if runaway inflation continues -- is to hold down federal spending. A favorite way of appearing to do this is to cut entitlement programs -- those costs of which are set by the number of eligible applicants -- below estimated costs and then to vote more later. Food stamps is such a program and the committee cut the administration's requests from $9.9 billion to $9.7 billion. In the past the administration's original proposals have always proved too little. t

The other bill would provide $4.8 billion for military construction in the United States and abroad it. It includes $97 million to continue design of the MX missile, which would be moved secretly from one launching site to another in a giant shell game in hopes an enemy wouldn't know where to shoot at it.

The three bills together recommend $37.7 billion in new budget authority plus $13 billion to agricultural programs in loans and transfers.

The bills are a total of $742 million below the administration's request. Most of that, $568 million, was cut from the military construction bill. One-third of that reduction was achieved by cutting back on housing for families of military personnel.

There are 13 basic appropriations bills in all each year. Congress has turned to these after adopting its balanced budget resolution last week. That resolution merely set targets. The appropriations bill will determine whether those targets are hit. Actually, almost all the experts expect the budget to end up well in the red again, as the recession raises costs and cuts revenues.

The pay raises issue also complicated the appropriations process last year, when Congress first decided to deny itself and senior employes in the civil service a raise, then finally gave itself and senior employes a smaller raise than others in the federal service -- 5.5 versus 7 percent.

The House also debated yesterday and may take final votes today on an urgently needed $15 billion supplemental appropriation bill to carry various programs through the rest of the fiscal year ending Sept. 30.

It includes $1.5 billion for a fund to pay jobless benefits to people thrown out of work by imports as well as money for depleted programs for black lung benefits and disaster relief. Nearly half the money is for pay raises in effect since last year. There is also $784 million to repair damage caused by the eruption of Mount St. Helens and $100 million for refugee assistance.

The bill was delayed for months until approval of the budget resolution for next year raised this year's spending ceiling enough to make room for it.

Meanwhile, Congress' tax-writing committees began drafting measures to comply with the budget resolution, which calls for more than $4 billion in increased revenues next fiscal year. But the committees steered clear of the controversial main revenue-raising proposal President Carter made, to withhold taxes on interest and dividends.

In initial drafting sessions, the House Ways and Means and Senate Finance committees also ignored other White House proposals, including tightening of the foreign tax credit.

Instead, the two panels came up with their own lists containing far less painful measures, from delaying a scheduled reduction in telephone excise taxes to creating a new tax to cover oil-spill cleanup costs to speeding up corporate income tax payments.

The Finance Committee tentatively approved two of the proposals -- a plan to tax the profits made by foreigners on land sales in the United States, and a requirement that workers pay income taxes in cases where their companies pay Social Security taxes for them.

On still another front, House leaders apparently reached an understanding and averted a clash over turf between two powerful committees -- a dispute that could have undermined the budget discipline that Congress imposed on itself just last week.

At issue is $500 million to continue Saturday mail deliveries that the House Appropriations Committee approved last week in seeming defiance of the budget resolution, which had assumed that money would be cut.

The House seems likely to approved the Saturday mail money, but Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) indicated he will somehow make it clear that the House is not retreating from its commitment to balance the 1981 budget.

That understanding, reached in an afternoon-long meeting between O'Neill and leaders of the feuding Budget and Appropriations committees, appeared to satisfy the request of Budget Committee Chairman Robert N. Giaimo (D-Conn.), for a show of support by the House leadership for continued budget discipline.

What will actually happen to Saturday mail deliveries after the new fiscal year start Oct. 1 is not entirely clear.

It could be eliminated in a package of spending cuts, drafted under the reconciliation process, later this summer. It is also possible that the Senate might reject the $500 million appropriation. Or, as some sources suggested yesterday, the Postal Service might be able to finance Saturday deliveries with a $250 million appropriation, with another $250 million to be cut elsewhere in the civil service-postal area.

Yet another possibility is that Congress might declare itself satisfied with half-a-loaf on the postal subsidy issue.

In a Budget Committee meeting yesterday, Giaimo conceded it would be fruitless to try to fight Saturday mail deliveries on the House floor, saying it would be wiser to wage the battle over the whole package of reconciliation cuts. "I'm fearful of the postal lobby," he said. "They have tremendous power."

As for progress on reconciliation generally, Giaimo said he understood that most committees charged with a responsibility for making spending cuts have indicated a cooperative attitude.