Boston Mayor Raymond L. Flynn yesterday accused the federal government of "walking away" from urban problems in Boston and other big cities.

In a Law School speech in front of 100, Flynn said that President Reagan's "New Federalism"--in which cities receive less financial support from the federal government but have fewer regulations to obey--is a "racial departure by the federal government from the cities."

"The federal safety net is no longer there," Flynn said in the half-hour Ames Courtroom talk, which was sponsored by the student-run Harvard Law School Forum. "There are large holes in that net that people are falling through."

The federal government, the mayor said, "is retreating and walking away" from urban problems like poverty, housing shortages, and poor educational facilities.

He said that while Boston's investment environment is highly favorable, downtown corporate wealth is not finding its way to the city's neighborhoods.

Despite the $1.69 billion invested in new Boston ventures over the last fiscal year, less than 30 percent of Boston workers making more than $15,000 a year are city residents, Flynn said.

In order to combat these problems, he said, cities must try to "build bridges" between prospering commercial districts and increasingly impoverished residential areas.

The mayor said his programs are providing such links between commercial and residential well-being.

Flynn cited as an example the requirement that commercial developers who want to build on choice downtown real estate also rehabilitate less desirable land. He also praised job-training programs for helping decrease the gap between the city's haves and have-nots.

He said cities must bear the additional responsibility created by federal policies. "We either do it ourselves or its not going to be done."