The Supreme Court agreed this week to decide whether the 6 percent commission charged by all real estate brokers in New Orleans violates federal laws against price fixing.

The court also dismissed Maiami's challenge to the constitutionality of a Florida property title act which effectively bars the city from claiming rights to some valuable land on Biscayne Bay.

The real estate suit was brought by four residents of the New Orleans area who used the services of brokers in buying or selling single-family homes.

Their antitrust suit against two New Orleans real estate associations, several firms and individual brokers was dismissed in U.S. District Court because they failed to prove services of a broker cannot be separated from interstate aspects of the transaction.

The U.S. Court of Appeals in New Orleans upheld the district court last Nov. 15. The appeal is from that decision.

The plaintiffs claimed that the 6 percent commission has a substantial effect on such interstate commerce aspects of real estate sales as moverment of home mortgage funds and obtaining property title insurance from out-of-state sources.

The plaintiffs also asked the court to decide whether pwersons buying or selling homes in the New Orleans area "and by implication, throughout the United States," should have the advantage of competition when they decide on a real estate agent.

To buttress their contention, the plaintiffs recalled that in 1975 the Supreme Court invalidated a 1 percent minimum fee charged by lawyers in Fairfax County, Va., for residential real estate title searches.

The real estate board replied that there is no requirement that real estate must be bought or sold with the assistace of a broker and that a broker's primary function is as an adviser to the parties in real estate transactions.

In the Florida case, the justices left intact the state's Marketable Record Titles Acts, which is similar to laws in 20 other states.

The action came in a case specifically involving 10.69 acres of downtown land, but the issue also affects some 100 other acres of land conveyed to the city years ago by the state.

The 1963 statute was designed to eliminate automatically with the passage of time old property title defects. With certain exceptions, it divests a landowner of his rights in favor of anyone having a recorded title for 30 years or more with no evidence of a conflicting interest.

At issue specifically in this case were 10.69 acres, part of bay bottom land conveyed to the city by the state in 1919 "for municipal purposes." The city says the Florida East Coast Hotel Corp., beginning in the 1920s, illegally filled in some of the submerged land.

In 1944, the city sold 10.69 acres of that property, along with 14 upland acres, to the St. Joe Paper Co.

Today, the Dupont Plaza Hotel is located on the land, as is a parking lot which is the proposed site for a high-rise project.

The Florida Supreme Court agreed with the city that the 1944 deed was void-that the city, and not St. Joe, owned the land at the time.

But the court said provisions of the Florida Marketable Records Title Act have extinguished the city's property ownership rights because it failed to assert its claim to the disputed land by 1974.

In a decision the city said was "unique" in this country's courts, the Florida Supreme Court said a "wild" or void deed is protected under the property title law.

Florida's top court ruled last October that the state law "can constitutionally be applied to bar the city's claim."