Conversion of rental apartment units into condominums is having a sharp impact on retirees all over Florida and has resulted in a flood of complaints to legislators. Many retirees assert that they cannot afford to buy their apartments nor can they find comparable places to which they can move.

The problem is particularly acute in Miami, Fort Lauderdale and in the Tampa-St. Petersburg area on the state's west coast.

Rik Fulscher, president of the National Apartment Association, in recent testimony before the housing subcommittee of the Florida House, pointed out that inflation and high interest rates, coupled with restrictive local building codes, zoning and slow-growth policies, have contributed to rental housing shortages and have generated pressure for rent control.

As a result, investors and developers are reluctant to build rental apartments.

Fulscher added that a study prepared in 1978 for the Joint Economic Committee estimated that during the 1980s, the nation would need an additional 9 million rental housing units. Current production levels are far short of this figure.

"By cranking in the normal attrition through abandonment and demolition," Fulscher added, "we wind up with a net reduction in the rental housing inventory this year, a rather bleak prospect in the light of the lowest vacancy rate in 20 years and the Joint Economic Committee study's estimate of 9.4 million rental-housing-unit demand for this decade."

In Dade County (including Miami and Miami Beach), about 10,000 of the county's 200,000 rental units already have been converted to condos. In the first two months of this year, Dade developers filed applications to convert 1,928 apartments to condos, almost half of the number converted during all of 1979. Another 8,000 are expected to go condo this year.

Earlier this year the village of Kings Creek in South Miami was sold for $33.6 million, one of the largest transactions of its kind in the county.

This rental project is being converted into 1,067 condominums. More than half of the current tenants have signed up to buy their apartments.

In another Miami transaction, Harold L. Miller, a Chicago attorney and investor, purchased a building for $13.6 million and has begun turning it into 161 condominums. Prices will range from $95,000 to $170,000 and Miller said he already is nearly sold out.

Nonetheless, he predicted that Florida conversions may be headed for a shakeout.

"Because of the heavy concentration of rental units in Dade, Broward and Palm Beach counties," he said, "it has attracted too many amateurs to the lucrative conversion field. Amateurs got into the conversion business because they saw it as a way to make money.

"However, they began to overbid on property. As a result, that forced prices to go up, yet they are still sitting around with units to sell."

Broward County (Fort Lauderdale, Hollywood and Pompano Beach) presented a more striking picture.

Applications during January and February covered 2,647 apartments, the equivalent of 84 percent of Broward's conversions for all of 1979. About 7,000 of Broward's 65,000 apartments have gone condo in the last three years and few people are willing to predict the final tally for 1980.

On a statewide level conversion applications in January and February this year covered 6,817 apartments, or 42 percent of last year's total.

Together, Dade and Broward counties, which have 44 percent of the entire state's rental units, produced a disproportionate share of the potential conversions, to two out of three.

Several municipalities have enacted ordinances so as to put a damper -- temporary as it might be -- on condo conversions. But officials agree that the final answer will have to come in the courts.

Lauderhill (Broward County) has declared a six-month moratorium on conversions while Lauderdale Lakes has imposed a 90-day moratorium. Nearby Hollywood has given preliminary approval to a 90-day moratorium.

In adjacent Dade County, Miami Beach and Bay Harbor Islands have imposed three-month moratoriums and North Bay Village, a 30-day moratorium.

Recently, the Miami Beach moratorium was struck down in circuit court even as others are being challenged by the developers. One city official remarked: "We're pretty well aware that we can't stop conversions. The moratorium is just a way to give us a little breathing space."