New Rule for Times Sq. Space

In a bid to preserve what remains of Times Square's character, the New York City Planning Commission yesterday approved a requirement that developers set aside for entertainment uses an equivalent of nearly 5 percent of the floor space in new or enlarged buildings.

The rule would apply to a core of mid-Manhattan from 43d to 50th Street, on both sides of Broadway and Seventh Avenue. If it is adopted by the Board of Estimate, it would affect any development for which the foundation is not in place by the time of the board's vote.

The requirement could be satisfied in a number of ways. Auditoriums, theaters, dance halls, eating or drinking places where there is entertainment, movie production studios, radio or television studios or music, dancing or theatrical studios could be built anywhere within the building - including basements and subbasements.

Developers could also satisfy the requirement with costume rental establishments, music stores, musical instrument repair shops, record stores or ticket sales offices. But these would have to be on the ground floor.

''These entertainment uses are already prevalent in the area,'' said Sylvia Deutsch, chairwoman of the Planning Commission, ''and we want to make sure that new development contributes to the maintenance of the special character of this unique and marvelous part of our city.'' Residents of Other Neighborhoods

The commission's unanimous vote on the measure came toward the end of a long and contentious day in which development was passionately debated by partisans from Turtle Bay in Manhattan, the Kingsbridge and Marble Hill neighborhoods of the Bronx and Bayside, Queens.

There was no public testimony on the Times Square measure yesterday. However, at a public hearing in July, a representative of the real-estate industry testified against the requirement that space be set aside for entertainment uses.

''Many potential tenants for office developments are wary of committing themselves to buildings which contain non-office uses,'' said Arthur Margon, senior vice president of the Real Estate Board of New York. ''We may not approve of this attitude, but it is real and it can substantially limit the potential field of tenants for new development in this area.''

Among those who deplored the attitude were Nicholas Quennell, a vice president of the Municipal Art Society, who said: ''We should look at conventional office use as the unwanted guest, not the future host, and make all decisions accordingly. As hosts, the corporate offices will inevitably impose their deathly respectability upon what has been -at its best - a somewhat raunchy but charming collection.''

Exempt from the measure approved yesterday would be a building with less than 60,000 square feet of space, a building in which more than half the space is used as a hotel and a building on a lot more than half of which is outside the core area.

Given the definition of the core area, the new requirement would also not affect the enormous office towers planned by the Park Tower Realty company on four corners of Times Square. These buildings are part of the city's and the state's 42d Street redevelopment project.

There are a number of projects in the works whose developers have already set aside space for entertainment uses. For example, the 44-story office tower that Ian Bruce Eichner is planning to build on the corner of Broadway and 45th Street would have a multiple-screen Loews movie theater.

To calculate the amount of space to be set aside, 50,000 square feet would be deducted from the total. In the case of a 500,000-square-foot development, for example, the amount of space for entertainment uses would have to be 22,500 square feet - or 5 percent of 450,000. Other Measures

The Planning Commission approved several other measures yesterday affecting the theater district. It simplified the process through which owners of landmark theaters would have to go to obtain a demolition permit and it eliminated the development bonus that had existed for construction of new theaters.

Before the theater district vote, hundreds of speakers descended on the hearing room at 161 Avenue of the Americas, between Spring and Vandam Streets, where the Planning Commission met yesterday.

Busloads of people from Bayside came to object to the proposed rezoning of 213th Street, from 36th to 38th Avenues, to permit two three-family dwellings where only two one-family dwellings are now allowed.

Another contingent came from Turtle Bay to support a proposal to change the zoning of mid-block areas between First and Second Avenues and Second and Third Avenues, from 48th to 59th Streets, to encourage development in keeping with the smaller scale of those areas.

Perhaps the largest group came from Kingsbridge and Marble Hill (a vestigial section of Manhattan within the Bronx) to denounce plans to build a 1,001-unit condominium complex called Tibbett Gardens at 230th Street and Tibbett Avenue Extension.

The Planning Commission took no final action on any of these matters.