In the darkly paneled office of his embassy on 16th Street yesterday, a relaxed Herbert Brewer, Liberian ambassador to the United States for the toppled government of slain President William Tolbert, was on the phone.

"Anything from Monrovia?" he asked. After a few moments and questions, he hung up. "Rumor of another coup being planned," he said with a smile and raised eyebrows. "Ohhhhh!"

Outside the red leather door to his office, in the time-honored Washington tradition of dissident groups occupying the embassy of the homeland immediately following coups, five members of the Liberian expatriot group lounged against the walls, chatting amiably with embassy staff that was carrying on business as usual.

"Those five?" said Brewer when asked about the occupying forces. "I let them in this morning. They said they wanted to have a presence here. Actually, they wanted my keys to the embassy and the files." He gave a short laugh and smiled. "But I wouldn't let them have them."

In the four days since the coup that saw an army sergeant overthrow the Tolbert government and put many former officials on trial, Brewer and the Liberian activists, all members of the Union of Liberian Associations in the Americas (ULAA), have been gently sparring over who is in control.

Late Saturday Brewer invited five ULAA members to his residence on Fulton Street to discuss the issues. But after a half an hour, 70 more ULAA members walked in and began an occupation that lasted until early yesterday morning.

"When I saw them, I figured that we wouldn't get anything done," said Brewer. "So I said, 'Why don't we turn this into a social affair?' I had my wife get out drinks and we arranged for everybody to sleep in the living room and wherever they could find a place. The last one left about 1 a.m. this morning."

Brewer said the impass there was resolved when he agreed to open the embassy yesterday morning and let two ULAA members use the facilities that included telephones and telex machines to keep in touch with events in Liberia.

"But then they brought five," he said shrugging. "That wasn't part of the agreement."

The occupying dissidents were clearly pleased.

"We represent the interests of the Liberian community in the United States," said Ignatius Clay, president of the ULAA New York chapter. He said that the 17,000 to 20,000 Liberians in the United States, many of them students, needed to have the embassy open and functioning and serve as a source of information on what has been happening at home.

President of ULAA Bai M. Ghala, a 40-year-old Liberian living in Minnesota, had flown here Monday after addressing a group of Liberians in Chicago, he said. "I passed the hat after the speech and got my plane ticket here," he said, smiling.

Three weeks before, he had been in Liberia to talk with Tolbert about changes he and others felt were necessary to stabilize the situation. Tolbert, he said, had not listened.

"It was one of the most repressive societies in the world," he said. "Only those descendants of the American slaves who came to the country were in positions of power. Everyone else had to do what they wanted."

No, he said, changes that have long been called for in Liberia may be in the offing.

The battle for control of the embassy goes on, he said.

"The ambassador did not want to open the embassy," said Gbala, who until last June was working in a Minnesota company that encouraged international trade. "I told him, 'Mr. Ambassador, this place must be open.' He refused to give us the keys because he said it was not diplomatic protocol.

Behind the doors to his office, Brewer reflected on his refusal by saying that "I know diplomacy. One European told me that Liberia ought to open a school for diplomacy because we are all so diplomatic. I take that as a compliment. He said the school would be filled with people from all over the world."

He said that he had received a tip Saturday that ULAA was planning to take over the embassy so he called the State Department and arranged for extra security. Outside the embassy yesterday three policemen stood guard, questioning those who approached but allowing anyone in who wanted to enter.

Now, he said, he is waiting for a telex from the government to tell him what to do. "I heard that I'm going to continue on as ambassador," he said. "But all the telex messages I have gotten so far are these: the complete speech of Sergeant Doe (the leader of the coup) and the announcement of the new cabinet."

He picked up the phone and called again. "Have we gotten any telexes?" he asked. "No Oh, it is 7 p.m. in Monrovia. That explains it."

In the hallway, Gbala discussed Brewer's possible fate in the embassy.

"If he is careful and cooperates with us," he said, "then he may be reappointed. But we will have to see how he handles the situation."