In the Byzantine politics of Capitol Hill where pork-barrel interests can determine economic policy, a set of deals made by the Reagan administration to win passage of $35 billion in budget cuts and enactment of the $749 billion tax bill came home to roost over the past two weeks.

The end result, as the House completed action on the farm bill Thursday, was to raise doubts in the minds of some Southern Democrats whether the administration and its congressional allies can live up to commitments. These commitments have centered on gut, parochial issues of major importance to the recipients.

At the same time, half by luck, half by political calculation, the Democrats were able to use the farm bill as a vehicle to demonstrate their ability to reward loyalty. This kind of political dealing, which is often subject to public criticism, is often essential in gaining congressional support for legislation. Developments over the past two weeks, combined with adverse economic news and internal disarray within the GOP, raise doubts about the continued ability of the Reagan administration to win significant new budget cuts this year.

"I think I could say, 'Beware of a Republican bearing a commitment,' " Rep. Billy Lee Evans said in an interview as the final votes were being cast last week.

The Georgia Democrat brought five of his colleagues on board the the Reagan tax-cut wagon back in July after getting what he thought was a commitment that the peanut program would receive significant backing from the administration and the House GOP. "I'd say in the future that if we do any horsetrading, I'd want them Republicans to go first."

Evans is one of the Boll Weevils, the faction of Southern conservative Democrats who provided Reagan with the essential margin of victory when the tax and budget cuts went through the House over the objections of the Democratic leadership.

But at the end of last week, Evans and a number of his colleagues were looking at the following political facts:

To win passage of the Gramm-Latta budget cuts--named for Reps. Phil Gramm (D-Tex.) and Delbert Latta (R-Ohio)--in June, and the tax cut bill in July, the administration promised to support whatever decisions were made by Congress on the sugar program and, in the case of peanuts, to actively back continuation of the program.

The result was strong block voting for the Reagan programs from Democrats in sugar and peanut states such as Louisiana and Georgia. In a comment that has become part of the folklore of the opening months of the 97th Congress, Rep. John Breaux (D-La.), a sugar proponent, said, just after he switched to vote for the budget cuts, that his vote could not be bought, but "it can be rented."

When the issues came to a crunch during House consideration of the support programs in the farm bill, however, peanuts went down the chute by a margin of 159 to 250. A majority of Republicans voted against the program (119 to 66), and sugar was defeated 213 to 190, with Republicans slightly in favor, 103 to 100. (Both programs are almost guaranteed to survive after a House-Senate conference, although the defeats are political blows to House members representing sugar and peanut-growing districts who cannot boast to constituents of their ability to protect local interests.)

At the same time, one of the most controversial programs in the farm bill, tobacco supports, survived the toughest challenge it has faced in recent history. The House voted 231 to 184 in favor.

In the politics of this vote, North Carolina Democrats, led by Rep. Charles Rose, called in every outstanding chit, the most important of which was their near unanimous support of the House Democratic leadership, and defiance of the Reagan administration, in the budget and tax fights.

In the key vote on Gramm-Latta II, North Carolina Democrats, unlike many of their Southern partisan colleagues, voted down the line against the Reagan administration, and on the tax bill they voted six to one with the Democratic leadership.

In return, House Speaker Thomas P. (Tip) O'Neill (D-Mass.), much of the rest of the Democratic leadership, many members of the congressional black caucus and even organized labor ended up actively supporting the tobacco price-support program. In the House vote, Democrats lined up in favor, 156 to 78. Republicans, despite requests for support from their leadership, voted 106 to 75 against the program.

In a brief exchange on the House floor, an opponent of the tobacco program, Rep. Robert W. Edgar (D-Pa.), asked: "Can we in fact spend one dime of federal money when we have reduced nutrition programs for many throughout our nation? Can we in fact spend one dime when we have reduced assistance to families of low income?"

Rep. W.G. (Bill) Hefner, a North Carolina Democrat, immediately countered: "I would just respectfully point out to the gentleman Edgar who was referring to the cost of the programs for the feeding of children and senior citizens and for cancer research, that there were many of us who stood and were counted to keep the money for these programs. . . We took a considerable amount of heat."

After the vote, and as Democrats began to crow that the farm bill was a demonstration of a revived Democratic Party, Rep. Trent Lott (R-La.), the GOP minority whip and a key participant in the negotiations for Democratic votes on the budget and tax bills, angrily denounced the opposition.

Democratic wheeling and dealing over the past 25 years in which special and geographic interests traded votes and expanded federal programs is "just what got this country into the trouble it's in," Lott declared. "Republicans are just fundamentally opposed to allotments and subsidy programs," he said.

Lott had been a participant in just the kind of dealing he denounced among Democrats. But his comments reflect the difficulties facing the GOP when the issues go beyond major questions of budget and tax cuts, and move into the trenches of specific programs that are important to key allies: A party committed to a policy of fiscal austerity is going to have difficulties making good on pork-barrel promises.

Another faction frustrating the austerity drive is within the GOP itself: Republicans from the Northeast and Midwest whose constituencies are, in many cases, dependent on the social programs facing the most severe reductions.

The farm bill votes came just as members of the House who have backed the Reagan program are showing increasing anxiety over continuing high interest rates, preliminary statistics indicating a growing rate of bankruptcies, and the report Friday that inflation in the most recent three-month period was running at an annual rate of 13 1/2 percent.

While the farm bill votes may demonstrate some of the problems facing the administration and the congressional GOP, Democratic claims that the outcome reflects a renewed party vitality were disputed in private by a number of the party's own members. They see themselves able to win some victories on the House floor, but without any real shared goals. "The only thing we have in common is incumbency," one strategist commented.