The field commanders of Ronald Reagan's presidential campaign managed their first assignment as signment as leaders of the Republican Party -- the writing of a party platform -- in a relaxed, confident style.

The Reagan forces decided in advance not to try to dictate every sentence in the platform, and partly as a result the document includes several potentially controversial planks that the candidate might not have approved. But essentially it echoes Reagan's views, and his lieutenants here declared themselves satisfied with the outcome.

Their relaxed approach to the process surprised some Republican veterans here, but one of them said today that "maybe they're right."

The outcome created an ebullient mood among the delegates who served on the platform committee. They ended their work today by approving an enthusiastic preamble to their platform that denounces President Carter and promises to "make American great again."

The platform committee was a strongly conservative group, representative of the strain of opinion that has predominated among party activists for years. Its virtual unanimity on all issues was striking, and veteran Republicans remarked on it throughout the week.

Bryce Harlow, who served in several Republican administrations, observed that the most controversial issue of the week -- ERA -- was resolved by a 90-to-9 vote.

Reagan's aides had several objectives in the platform-writing process: to encapsulate their candidate's views, enthuse the members of the platform committee and, by extension, Reagan loyalists around the country, broaden Reagan's appeal and try to avoid pitfalls that could prove hazardous to Reagan in the coming campaign.

On the last two points their success was less than total. Early in the week, Reagan's principal foreign policy aide. Richard V. Allen, sought to defuse one potential problem involving Taiwan, and apparently succeeded. Contradicting earlier statements by Reagan, Allen announced that the candidate has no desire to restore full diplomatic relations with Taiwan, and does not want to "turn the clock back on U.S. relations with the People's Republic of China.

The United States gave full recognition to the PRC early this year, simultaneously downgrading relations with Taiwan to a semifictitious "unofficial" status. It was a face-saving device for Peking, but one the Chinese have repeatedly said is crucial to continued good relations with the United States.

Reagan associates here feared that this new position on Taiwan might not be acceptable to the staunchest conservatives on the platform committee -- Sen. Jesse A. Helms (R-N.C.), for example. But a fight on the issue was avoided, and Reagan apparently has extricated himself from a risky stand on China.

On domestic social issues, the draft platform that the Reagan camp approved before this week's meeting began sought through verbal gymnastics to affirm Reagan's support for a constitutional amendment banning abortion and his opposition to the Equal Rights Amendment without offending people on the other sides of those issues.

The platform committee wanted to be more explicit, and thus less accommodating, on both issues, and this sentiment prevailed.

The Republicans will carry into the election a platform that challenges what the polls say are majority positions in the American electorate on these two sensitive issues.

Senior Reagan aides acknowledged this week that the outcome was less than ideal, but they also said that the platform accurately reflelcts Reagan's position on both issues.

Several Republican politicians from the Nixon and Ford administrations who have been invited recently to help the Reagan organization here agreed that after this week of platform-writing it is incumbent on Reagan to make serious overtures to the moderate wing of the party and, by implication, to the independents and Democrats he will need to win in November.

Reagan should begin making such gestures "with some dispatch," said Harlow, predicting that Reagan would do just that. Another Nixon-Ford era official said it is more necessary for Reagan to make those gestures now than it was a week ago, before the platform committee began its work.

Reagan aides here said they had every intention of accommodating Republicans and others who had not been part of Reagan's entourage in the past. This attitude was expressed by Jim Brady, Reagan's director of communications, who described the candidate's approach like this:

"Where there is fire, we will provide the water. Where there is burn, we will provide the balm."

According to Lorelei Kinder, Reagan's adviser on women's issues, this attitude motivated efforts by Reagan operatives this week to make a modest change in the ERA plank to assuage the feelings of staunch ERA supporters. Kinder said she inaugurated negotiations that led to the insertion of a sentence in the plank which recognized as "legitimate" the efforts of both pro- and anti-ERA elements in the Republican Party.

This was a far cry from reasserting the party's support for ERA, which had been in GOP platforms since 1940. But it did improve the atmosphere in the platform committee, and may have helped convince the pro-ERA forces to abandon their fight.

The essential ingredient of this platform week in Detroit may have been the general presumption shared by all the Republicans here that they are launched on a campaign that will end with Reagan's victory.

"Their harmony is quite exquisite," as Harlow put it -- a harmony born of confidence, and which the Republicans here don't want to squander no matter what their differences on abortion and the ERA.