MIAMI BEACH--The transformation which by late yesterday had turned the Doral from a plush resort hotel to Senator George McGovern's frantic campaign headquarters began here Saturday.

Wires snaked across the carpeted lobby, parking lots filled with staff cars and TV mobile units. What had been a tidy meeting room became the McGovern operations center, desks twitching with the action and sound of telephones, typing and talk.

McGovern arrived here Saturday at 3 p.m. The weather was stormy, McGovern was confident. "Now in all probability, this will be a hard fought campaign...but we intend to conduct ourselves from this moment forward with dignity," he said.

At a press conference immediately following his arrival. McGovern told reporters at the Doral there could be no compromise on the California challenge which threatens 151 of his delegates. "The American sense of fair play and rule of law are now in the hands of delegates," he said, but he also said he was confident that he would win.

Throughout the afternoon, McGovern was assaulted by throngs of reporters. Saturday night he conducted staff meetings which held die-hards until 4 a.m. By Sunday the confidence had worn thin when he met the press again in the morning with Rep. Ronald Dellums (D-Calif.), McGovern had stopped stating and started proclaiming. "The issue at stake here is not simply the future of a single candidate, but the future and the integrity and the quality of the odest and largest political party in this country."

Democratic National Chairman Lawrence F. O'Brein's ruling that 1433 delegates and not 1509 would constitute a majority in deciding the California challenge came as a comfort to McGovern forces, except that by yesterday, the whole California question had become a chicken and egg type of problem. The 1433 figure would undoubtedly be challenged by stop-McGovern forces, yet who would vote on what the majority of those eligible to vote was to be? And who was eligible to vote in the preliminary rule voting?

The McGovern staff left these problem to the Democratic National Committee and went intently on its business of talking to delegates--pleading, cojoling, coaxing. One Nevada delegate who described herself as "wavering" said she had received over 30 phone calls Sunday from both parties in the California dispute.

Sunday night, the McGovern staff poured into the Doral Hotel for yet another staff meeting, and a late reading on the programs made that day. It became difficult to get elevators, and when they came they were filled with McGovern staffers who wore white staff buttons, good only for the mezzanine operations room, and the coveted red staff buttons which get you onto the 16th floor.

To get beyond that to the penthouse where McGovern and his top staff hold out, you've got to be very smooth or very important. The Secret Service stops all traffic on the 16th floor. Secret Servicemen don't bluff. They are everywhere--in boats, helicopters, bushes and cars, and cordoning off the stairwell of the hotel.

The last word from the McGovern staff before the final meeting to prepare Monday's struggle was from campaign aide Pierre Salinger who admitted that there might be problems if a majority of 1509 was to decide the California challenge, but there would be none with a 1433 figure. Either way, he was still talking confidently. "I don't share the general feeling that it's first ballot or nothing," he said.

Throughout Sunday night and yesterday, McGovern volunteers were left to mimeograph, find and call. Onlookers milled in the brilliantly lit lobby of the Doral admist the fake Louis XIV furniture, and the McGovern staff, high stop the green glass flanks of the hotel, directed the massive California effort which groped frantically through every bleached hotel lobby along the beach