New York — Concluding that the nation's cities ''are suffering unduly'' from the Reagan administration's budget cuts, the mayor of America's biggest city says he will step up his criticism of President Reagan's economic policies.
With the exception of two critical addresses, the most recent at a conference sponsored by the National League of Cities in Detroit, New York's Democratic Mayor Edward I. Koch has been nearly alone among big city mayors in his support of President Reagan.
In recent months, however, he said in an interview with the Monitor here, he has begun to sharply criticize Mr. Reagan's policies - not in an effort to change them, because he doesn't believe the President will do that - but as a means of influencing the course of the 1982 congressional races.
At the same time, he concedes that the city and the nation have gained a good deal in many ways under the Reagan administration.
However, Mayor Koch would not go so far as to say the Reagan administration is a ''net gain'' over the Carter administration, as he forecast in a year-end interview with this newspaper last year.
He did stress, in his usual emphatic style, that the past year showed that the current administration's policies have not worked.
''Even though I didn't vote for Mr. Reagan and disagreed with his concept (economic policies), I hoped it would work,'' he said. ''But it isn't working and won't work. . . . While I don't feel my comments will influence President Reagan in his decisionmaking . . . I do believe where we can have an impact is on the Congress - 435 members of the House are running and one-third of the Senate and they have to know they may lose unless they change the policies of the country.''
Two other reasons for Koch's outspoken criticism seem to be rooted in his own personal political triumph and ambition. In the November general election, the lanky mayor chalked up 76 percent of the vote, more than any mayor in New York history. And he won every single election district, even predominantly black and Hispanic election districts which had shown much-publicized unhappiness with Koch's city budget cutbacks. In addition, the mayor has vowed that he will conduct his second term, which begins Jan. 1, as if it is his last - without any concern for political consequences.
''If I don't have the same energy level,'' he says of the possibility of seeking a third term, ''or the job doesn't have the same challenge, then I will not run . . . .
''I think the challenge will be there.''
Asked if his efforts to step up his criticism of President Reagan's economic policies threatens what he calls a ''good relationship'' with the President, the mayor said no.
''I don't think I've jeopardized my relationship with the President. I'm always quite civil. And the difference between what others do and what I do is that I praise policies when I think they are right. . . . In reducing the federal mandates on localities, the Reagan administration has done a terrific job. And I'm for a strong military defense, even though I disagree with the way they are pursuing it. I think the President is a man of courage and integrity and keeps his promises. I say all that and then when I disagree, I disagree in civil terms, as opposed to personal attacks.''
These ''mandates'' Koch spoke of refer to federal laws that require the city to provide programs, like sludge removal or special education for the handicapped, and then pick up the cost beyond the federal funds allocated.
On the other hand, Reagan budget cutbacks have taken a severe toll on the city's ability to improve its mass transit system. Nonetheless, the mayor said he was confident that there would be ''marked improvements'' in the subway system.
To this end, he said, the city plans to spend just under $10 million over the next three years on mass transit improvements.
What the city plans to spend and what it actually does spend can be two different things. For example, in a report just released by the city comptroller , it was found that city spending on capital improvements construction was far behind the original plans.
''We're not going to see a major change in the subway system for two years,'' the mayor said. ''I'm talking about a major change that is marked by new rolling stock (subway cars). We need these to replace the damaged cars which have been taken out of service. . . . We don't have enough cars that work. The new cars will start coming on line in two years.''