A week of open combat in the Republican Party ended today when Ronald Reagan announced that Bill Brock would remain party chairman.

It was a victory for the party's congressional wing and former president Gerald R. Ford, who had strongly urged Brock's retention. But the Reagan campaign will have a stronger hand in national committee operations now.

Reagan announced that Drew Lewis, a Reagan campaign official and the national committeeman from Pennsylvania, will become the committee's deputy chairman and chief operating officer.

Lewis is to keep his post on the Reagan campaign committee and serve as the candidate's liaison on the national committee in an effort to integrate the two operations.

Reagan tried to minimize the conflict that had torn apart the GOP over Brock, blaming the whole affair on "Washington rumor mills" and saying that his national chairman, Sen. Paul D. Laxalt (R-Nev.), had never really wanted to get rid of Brock.

"Everyone was running around like Chicken Little saying that the sky is falling," Reagan said. "There was no foundation for those rumors."

In fact, Laxalt had openly advocated Brock's removal in statements to various newspapers. Also, a report by Reagan's New England coordinator, Gerald Carmen, was highly critical of Brock's performance and advocated his replacement.

Some key decisions at the national committee may simply have been postponed by today's announcement. Brock said he would wait until the national committee and Reagan's campaign committee are integrated before making any decision on the fate of several aides who had been the chief targets of the reaganites.

But the inclination here seemed to be to avoid any appearance of a political purge.

"The whole thing is a big confusion, a big misunderstanding," said Reagan campaign director William J. Casey. "It's all cleared up now." Casey, chief of staff Edwin Meese and communication aide Lyn Nofziger attended today's meeting with Reagan, Brock and Lewis.

The lines of the compromise were described earlier in the week when Brock indicated he was "very willing" to work with Lewis, a respected party professional who managed Ford's Pennsylvania campaign against Reagan in 1976.

It was evident today that Reagan was trying to avoid portraying Laxalt, a personal friend, as a loser in the intraparty battle. Laxalt was campaigning for reelection in Nevada, and Reagan said his statement today reflected Laxalt's feelings as well as his own.

"Bill Brock and I have been in agreement for sometime that he can serve best the interests of the party and my campaign by staying on as national chairman," Reagan said.

Reagan's action today was an effort to restore order in a campaign that has been sputtering ever since he clinched the nomination last month.

In the week before the final round of primaries, Reagan aides talked confidently of using the month of June to consolidate and broaden the campaign effort in a way that would demonstrate Reagan's acceptance to all segments of the party.

Instead, the campaign has been rent by infighting as old and new aides jockeyed for preferred positions.

Some of the battles have been ideological, recalling the days of the mid-1960s, when the Republican Party was torn between conservative and moderate wings. Others have been purely personal.

The man in the middle in most cases has been campaign director William J. Casey, who is highly regarded for bring fiscal order to the campaign since he took over Feb. 26 but who lacks national political experience.

Casey, onetime chairman of the Securities and Exchange Commission under Richard M. Nixon, is described by one Reagan operative as being "highly decisive in different directions on different days."

The campaign's issues and communications divisions are still not operating at full speed. Some Reagan intimates also are concerned that valuable time is being lost in preparing the candidate for the intense issues scrutiny they believe he is likely to face in the fall campaign.

Reagan has been at home this week, attending a series of staff meetings at which the general election campaign plan is being discussed. He is scheduled to travel east next week for a series of party dinners and editorial board meetings in New York and Washington.

But where three weeks ago Reagan would have been traveling with the aura of a victorious nominee who had swept away all opposition, he now ventures forth into what is historically his most difficult region with party leaders wondering whether he will divide or unify the GOP in the fall. p

Memories are still strong in New York and Pennsylvania of the heavy toll taken of Republican office-holders when Sen. Barry M. Goldwater (R-Ariz.), headed the ticket in 1964.

Reagan, who launched his national political career in that campaign with an effective television speech for Goldwater, campaigned for Republicans of all persuasions in his day as California governor, and had many moderates in his administration.

"What is happening here is not Goldwater revisited," said one Reagan aide this week. "What is happening, frankly, is that the governor has not asserted himself and insisted on a harmonious, unified campaign."

Critics of reagan is Sacramento often said he had a tendency to drift and not involve himself in conflicts until they reached an advanced stage. The worry now in some segments of the Reagan camp is that this seeming indecisiveness may come to be seen as a reflection on how reagan would operate the presidency as well as the campaign.

The prevailing view among Republican leaders would seem to be that there is time to correct there deficiencies if they are perceived by the candidate.

The most encouraging note so far, the Republican optimists say, was former president Ford's enthusiastic endorsement of Reagan is Rancho Mirage last week.