A group of conservative religious and political leaders urged President Reagan yesterday to step up the government's enforcement effort against illegal pornography and to appoint a White House coordinator to oversee it.

The president, in a private 35-minute session with the group, Morality in Media, listened "very" receptively to their complaints that pornography laws are not being enforced adequately, White House aide Morton Blackwell said afterward.

Reagan told the group that his administration had "identified the worst hazardous-waste sites in America--we have to do the same with the worst sources of pornography," according to Blackwell and other participants in the meeting. He made no firm commitment regarding a White House anti-pornography coordinator, Blackwell said, but promised to give the suggestion "serious consideration."

"The problem is the $6 billion sex industry, which is developing at an alarming rate and at the present time is moving into cable television and the American home, so there is a critical situation here. And that was the immediate reason of this meeting with the president," said the Rev. Morton Hill, national president of Morality in Media.

The group appealed to Reagan for better enforcement by the FBI, Justice Department, Postal Service and Customs Bureau against illegal pornography. "We must get the most from the laws already on the books," Reagan was quoted by participants as telling them.

After listening to warnings about pornographic films being broadcast on cable television, Reagan reached back to his Hollywood experiences, the participants said.

He lamented that today's films are sexually more explict that those of his day. He recalled one scene with Doris Day in "Winning Team," in which the camera first filmed him and then her in bed, but never the two of them together.

He also said that "there are risks in censorship," but recalled approvingly the voluntary efforts at screening films that the movie industry adopted in the 1950s.

Among those expressing concern about illegal pornography yesterday were Cardinal John Krol, the Roman Catholic archbishop of Philadelphia, Ben Armstrong of National Religious Broadcasters, Wendell Ashton, publisher of The Deseret News in Salt Lake City, conservative political activists Howard E. Phillips and Richard Viguerie, Thomas Murphy of General Motors and Adrian Rogers of the Bellevue Baptist Church in Memphis.

Blackwell said Reagan singled out for praise Henry E. Hudson, commonwealth's attorney in Arlington County, for his pornography-fighting efforts.

Staff writer Michael Getler contributed to this report.