It will cost in excess of $16 million to renovate RFK Stadium to make it attractive for the owner of a baseball team, Frank Smith Jr., chairman of the D.C. Baseball Commission, testified during a Senate Commerce Committee hearing yesterday.

Even without some of the luxury items, the bare minimum it would take to convert RFK Stadium into a baseball configuration is $5.5 million, Smith said later in an interview, because rust has frozen the tracks intended to make seats interchangeable for football and baseball.

In a proposal prepared for the commission by the staff of the D.C. Armory Board, which manages the stadium, the following improvements would have to be made, according to Smith and Jim Dalrymple, the Armory Board manager who prepared the report:

* The demolition of approximately10,900 fixed seats and bleachers, replacing them with retractable seating that would increase football capacity by 2,703 seats and baseball capacity by 1,473. Estimated cost: $4 million.

* The elimination of the current mezzanine seating, to be replaced by 52 luxury sky boxes. Estimated cost: $2.3 million.

* The addition of elevators and escalators at Gates A and F. Estimated cost: $550,000.

* The construction of a "club" seating area for 500 at the mezzanine level plus the expansion and improvement of the current Sports Lounge. Estimated cost: $1.250 million.

* General improvements, including locker rooms, ticket office, restrooms and concession stands. Estimated cost: $1.7 million.

* General repairs of the roof, concrete parking lots and painting of the superstructure. Estimated cost: $1.177 million.

* Improvement of office and storage areas. Estimated cost: $1.5 million.

* Design, engineering and installation costs: $2.048 million.

Smith, a D.C. city councilman, said he is hopeful of major league baseball granting a National League expansion franchise to Washington by the end of this year. He said improvements could be finished in time for the 1987 season. They could not begin until the Redskins complete their 1985 season, he said, since construction would take eight months.

Who will pay for the improvements -- whose cost approaches the $19.8 million it originally cost to build the stadium which opened in 1961 -- remains uncertain. D.C. government officials want the Interior Department to give the city title to the stadium. The House passed such a law last year, but it died in the Senate.

With the city having title to the stadium, it could do one of two things: float a bond issue or lease the stadium to someone like Jack Kent Cooke, Redskins owner and the man most likely to get an expansion franchise here. Cooke has said he would make the necessary renovations if the city leased the stadium to him. Cooke was unavailable for comment yesterday.

Under the current plan, "telescopic," or retractable, seating would be installed from beyond third base all the way around to the right-field corner.

The estimated cost would be decreased by $1.250 million if the decision is made to continue using a natural grass playing surface. The cost to expand the grass field is estimated at $250,000.

Smith testified that he estimates a baseball team would yield about $600,000 annually in admissions taxes to the city and that a team's impact on the city would be about the same as the new Convention Center, enhancing hotels, restaurants and concessions by about $40 million.

Smith was among a number of representatives of local and state governments testifying yesterday on two bills that would give football, basketball, ice hockey and soccer professional sports leagues a limited but comprehensive antitrust exemption in the areas of franchise relocation and revenue sharing.

A major difference in the bills being considered by the Commerce Committee is whether expansion should be mandated by Congress.

The bill introduced by Sens. Thomas Eagleton (D-Mo.) and John Danforth (R-Mo.) gives the leagues antitrust exemptions so they can enforce relocation rules, keep out undesirable potential owners by a majority vote and share all revenues. The bill introduced by Sen. Slade Gorton (R-Wash.) mandates for expansion of at least two baseball franchises by 1988 and four NFL franchises by 1990, including teams in Baltimore and Oakland.

Danforth, the chairman of the Commerce Committee, asked Smith if he thought it was necessary for Congress to mandate expansion. "I don't want my city punished because I came down here and supported something they (baseball owners) are opposed to," Smith said.

The Maryland delegation, still smarting over the loss of the football Colts to Indianapolis a year ago, came firmly in favor of Gorton's bill, which is least favored by any of the leagues.

Mayor William Donald Schaefer of Baltimore, who said his city will lose $35 million worth of business annually as a result of the Colts' move, brought a sign that said: "Spare Other Cities What We've Been Through."

Rep. Barbara Mikulski (D-Md.), House sponsor of a bill identical to Gorton's, said, "We have to be as competitive to get sports teams as we do to get shipyard contracts. We find that when we debate this legislation, very often we're told that the United States Congress has no place in the issue of sports teams.

"I disagree with that, because we find that sports teams come to the government for the sole purpose to ask for guaranteed, fancy, often lavish, luxurious sports arenas. They want guaranteed ticket sales. They want state and local exemptions, and in the case of Louisiana (the NFL's New Orleans Saints), they even wanted the state legislature to put up a substantial amount of money.

"Then, they come to us for an antitrust exemptions, and they call that free enterprise. I don't call that free enterprise. We think that's looking for a free ride."