Treasury Secretary W. Michael Blumenthal all but predicted yesterday that New York City will find a solution to its short-run financial problems that will enable him to approve a $255 million loan.

"Bankruptcy is not a viable alternative (to the city's problems)," Blumenthal told reporters. "Unlike others, we are not saying to New York: 'If you want to go broke, that's not our problem.'"

New York City officials, in pressing the federal government to come through with a loan authorized by the Seasonal Financing Act whirl expires next year, have said if they don't get the money by Friday of next week, they won't be able to meet the city payroll and other bills.

But Blumenthal reiterated his position that he can't approve the loan request unless there is a prospect of repayment. And to make that prospect a reality, he said, the New York City authorities, the banks and union leaders "have to come together" of solve the city's problems.

He intimated that as soon as that is done, federal funds can be released.

"But President Carter never intended a black check - that would be a grave misunderstanding," Blumenthal said.

He specified that the Carter administration is demanding two things from New York. First, there must be evidence that the city can balance its fiscal 1978 budget. And second, the city, private banks and unions "must find a solution" resulting in paying off nearly $1 billion in notes, a requirement stemming from a court order rejecting a moratorium on those notes.

"This is not a game of 'chicken'" to force New York politicians to toe the mark, Blumenthal said in response to a question. "There are real problems, and serious efforts must be made to meet them . . . I see no reason why they can't be," he said. "(and) I'm sure they can find a solution."

Blumenthal said that to solve urban problems common to New York and other large cities in the long run, a new "federal urban bank or other financing method" may be needed to help cities, and improve their access to capital markets.

To deal with the "endemic" problems to high taxes and loss of industrial establishments, many approaches will have to be considered. Blumenthal mentioned reform of the welfare system, general tax reform, and the possibility of taxable local bonds accompanied by a federal subsidy as an alternative to tax-exempt bonds.