The simple blue plumbers cap that Juan Ojito put on on the other day was as symbolic as a king's newly placed crown.

Juan Ojito, 36, had just got a job, his first in the United States.

Here from Cuba only two months, he has become a U.S. taxpayer and a bit player in a cast of many thousands of political refugees who have converted Miami into a modern-day Ellis Island.

Miami has become such a haven for refugees that newcomers like Ojito, his wife and two children, speaking no English, blend in quickly and soon are faces in the American crowd.

Now Miami-Dade County is girding itself again for a new influx of Cubans from among the 10,000 who took refuge in the Peruvian Embassy in Havana two weeks ago.

After the drama in Havana is played out, local officials here assume that many of the 3,500 to whom President Carter has promised asylum in the United States will settle in this area.

The first of the refugees may not arrive here for some weeks, but the idea of a new wave of immigrants causes only minor blips on the official screen of anticipation.

Years of experience in dealing with a tide from Castro's Cuba that has ebbed and flowed since 1959 has created an infrastructure for moving refugees quickly and smoothly into the community.

"We have an airport facility for processing and moving the newcomers," said Tony Ojeda, an assistant county manager. "Every couple of weeks or so in the last year we have had flights of about 150 people coming from Havana.

"Once they are processed, we take them to a large county park where they can meet their families and begin to disperse into the community. We'll use the same procedure with those of the 3,500 who come here."

Although the process is smooth, the problems are large -- a shortage of housing being the most acute. "There's just nothing available for these people," Ojeda said, "although the state says it will help on housing."

An estimated 10,000 Nicaraguans who fled the Sandinista revolution, about 25,000 Haitian "boat people" who have come to south Florida in the last decade and other Latin emigres have intensified the demand for low-cost housing and social services.

"We view the problems as a federal responsibility and we feel the federal government should pay the expenses of handling refugees," Ojeda said. "We are really at the mercy of other governments and events in other countries and it is impossible to expect Dade County to deal with it."

Federal money covers most costs of dealing with Cuban refugees, including subsistence stipends they receive, and some help has come on nutrition and health care for the Haitians. Churches and other private groups provide social services, yet the strains are considerable.

Ojeda heads a county task force to oversee the Cuban's relocation; another assistant county manager over sees Haitian affairs. But the overall influx has become so pressing that County Manager Merrett Stierheim recently set up a committee to deal with all refugee matters.

Until now we've had two railroads running on separate tracks, but now we will have a county-wide south-Florida committee to look at a strategy for all refugees. It is a time of rapid change and tensions for local governments, and there is tension and back-lash in these communities." Ojeda said.

His point was underscored in a taut little exchange the other day in the office of the U.S. Immigration and Naturalization Service.

An INS secretary, a long-time Dade County resident, was complaining that the Cubans converted Miami from the "nice" place she remembered in the 1950s to a teeming metropolis that is being "dragged down" by strange people and tongues.

She was overheard and interrupted by a young Cuban-American, who spouted statistics about Miami's growth and prosperity since the Cubans began arriving. "It's a disgrace for people to have these attitudes at the immigration service," he said.

There is no question that Dade County is a far different place than it was 20 years ago. About 33 percent of the 1.5 million population is Hispanic, 15 percent black. The city of Miami is 56 percent Latin, with two Cuban-born commissioners and a mayor of Puerto Rican ancestry.

"In 1960 this was an economically depressed area, reliant on tourism, but in 1980 it is stable and growing, due in large part to the Cubans who have come," said Cuban-born Ojeda.

"The influx has been superbly positive. Miami has become a banking and trade and investment center, a busy port and growing tourist attraction. It's a very fast city, very fluid and moving, with a lot of opportunity."

The story of most of the Cuban refugees parallels that of Juan Ojito, who within two months of landing here had his children enrolled in school with special language classes and had found a job as a plumber's assistant.

The Ojito family found refuge in the crowded but tidy home of a sister who arrived in 1956. Last week, they were joined by two more newcomers from Cuba, Andres Medina, 37, and his nine-year-old son.

Ojito and Medina, boyhood chums, each spent six years in prison for political conspiracy against the Castro regime. When Castro in 1978 announced a plan to allow ex-prisoners to emigrate, they signed up to leave.

They talked for several hours the other evening about prison torture and the hardships of daily life in Cuba. It had been grim and they seemed a little amazed that they were sitting in a dining room in Miami, drinking unrationed coffee.

"It is divine to be here," said Ojito. "I do not have words to describe the help of the U.S. government."

"I am like a baby again, reborn here," said Andres Medina.