City officials said they would put the operation of those two concessions through normal bidding procedures, but would require that prices at the rink be kept ''moderate.''

The city's Parks Commissioner, Henry J. Stern, said it cost $2.50 to skate at the rink in 1980, and he hoped the price would not be any higher than that.

Mr. Trump said he would probably submit a bid and indicated that if he won the contract, he would turn any profits over to the city to benefit the homeless.

''If it's done beautifully, if it's done majestically, people will come back to the rink,'' Mr. Trump said. ''I think it can be profitable.''

The agreement with Mr. Trump is subject to the approval of the Board of Estimate by a two-thirds vote. In most cases, the city must choose contractors through a competitive bidding process if the cost of the project is more than $10,000. But in unusual circumstances, the board can forgo competitive bidding. Mr. Koch said he expected the board to do so. 'I Don't Want to Be a Wise Guy'

Asked why he wanted to take on such a project, Mr. Trump, who built Trump Tower on Fifth Avenue and who owns two Atlantic City casinos, said it was the ''last thing I wanted to do, actually.'' But the project was complex, he added, and he wanted to see the people have an ice rink.

''I don't want to be a wise guy and say I want to see my son skate there before he grows up,'' he said.