Ronald Reagan is leaning strongly toward keeping Bill Brock as chairman of the Republican National Committee and is seriously considering shifting his campaign headquarters from Los Angeles to Washington to ensure close coordination with the Republican Party machinery, informed sources here and in California said yesterday.

The informal word of Reagan's plans, if he is the GOP nominee, came as Brock prepared today to announce a lineup of Republican convention speakers that will put former president Gerald R. Ford in the spotlight on opening night, Monday, July 14, in Detroit.

Brock said in an interview that Ford will launch the convention and that the official "keynote address" will be shifted to Tuesday night, July 15, with the name of the speaker to be made public today.

The former president's speech is expected to be both a plea for Republican unity behind Reagan, the man who challenged him for the nomination in 1976, and a castigation of the record of President Carter, who took the White House from Ford in that election.

The apparently firm decision by Reagan to keep Brock in the party chairmanship and the serious consideration being given to a shift of his own headquarters to Washington are part of the general-election planning that is taking an increasing share of the time of the candidate and his high command.

Campaign Chariman William J. Casey and political strategist Richard B. Wirthlin have spent the past few days working on a general-election campaign plan that is to be completed by early June.

The shift of focus reflects the confidence in the Reagan camp that he may wrap up the votes for the Republican nomination even before the June 3 "grand-slam" final day of the primary season, when California, Ohio, New Jersey and five other states pick delegates.

After winning three of four primaries Tuesday, Reagan has at least 807 of the 998 delegates needed for nomination, compared with 177 for George Bush and 133 that are scattered or uncommitted. Bush has said he plans to stay in the fight through the last round of primaries, but the Reagan camp's internal calculations suggest he can wrap up the remaining delegates in the May primaries and caucuses.

The reported decision on keeping Brock in the party charimanship he has held for the past three years has both symbolic and practical significance for the Reagan campaign.

Symbolically, it is the first of several tests -- including the tone of the Republican platform and the choice of a running mate -- that will subject Reagan to cross-pressures from his original conservative cadre and from the broader cross-section of Republican constituents.

Conservative activists have been hoping that Reagan would replace Brock with a chairman from his own political camp. Brock, who was defeated for reelection to the Senate in Tennessee in 1976, won the chairmanship on the third ballot in January 1977, over Richard Richards of Utah, who had Reagan's backing.

Later in 1977, Brock clashed with Reagan and Sen. Paul D. Laxalt (R-Nev.), a key Reagan backer, when Brock refused to allocate $50,000 of party funds, which Reagan had helped raise, for a speaking tour Laxalt and Rep. Philip M. Crane (R-Ill.) were organizing against the ratification of the Panama Canal treaties.

Laxalt said at the time that the incident "reaffirms my feeling that if we are going to be effective as conservatives, it will have to be outside the RNC. It's obvious they're not sympathetic to our goals."

But Brock, while remaining neutral in the GOP nomination contest, has developed a good working relationship with Casey and, in the end, pragmatism and practicality have apparently triumphed over the pressure to install a chairman more politically and philosophically attuned to Reagan.

Sources here and in California said Casey had concluded after meetings with Brock and his staff that the RNC was well-organized for the coming campaign.

They said that, in management terms, it was felt that it would be hard to get better performance in the short period of the campaign from what has grown into a $24-million, 320-employe organization than Brock and his top assistants are likely to provide.

Similarly practical considerations -- such as the avoidance of the three hour time difference between Washington and Los Angeles -- are pushing toward a move of the Reagan headquarters to the capital, but that decision reportedly will not be made final until the entire campaign plan is reviewed early in June.