Religion will be a key issue in the next courtroom challenge to restrictions on federally funded abortions for the poor.

Backers of federal abortion aid are preparing to complain to a U.S. district judge in New York that the new congressional restrictions signed into law last week are rooted in religious belief - particularly Roman Catholicism. The restrictions impose one religious viewpoint and have no secular purpose; therefore, they violate the constitution's order against mixing church and state, the complaint will say.

Msgr. James McHugh director of the catholics' pro-life activities, said in response. "We hare not going to be intimidated by lawsuits, threats or harassment from individuals or organizations. Every church has a right speak out on human right issues and human dignity. The Constitution was never intended to silence the churches in this democracy."

The new law permits federal Medicaid to pay for abortions if the woman's life otherwise would be endangered: in cases of promptly reported rape or incast; and when two doctors determine that motherhood would result in severe, long-lasting health damage.

The suit by the Carter for Constututional Rights will be tried before Judge John Dooling, who enjoined implementation of earlier legislation.

Moves by pro-abortion groups also are expected in state courts and legislatures across the country.