Relatives and friends of the four American churchwomen slain in El Salvador two years ago said yesterday they are dropping efforts to participate in the trial of five soldiers charged with the slayings.

They said they have been unable to find a Salvadoran attorney to represent them, and they contended that the trial proceedings are designed to cut off any further investigation into the possible involvement in the murders of high Salvadoran military or political figures.

"We believe that the trial as it is designed to be carried out cannot lead to justice," said Sr. Helene O'Sullivan, director of the Maryknoll Order's Office of Social Concerns, at a press conference here yesterday.

Two of the slain women were Maryknoll nuns.

All the Salvadoran lawyers the families contacted in a six-month search declined to accept the case because they feared for their lives, according to Michael H. Posner, executive director of the New York-based Lawyers Committee for Internatonal Human Rights, which is assisting the families.

A U.S. attorney cannot appear in Salvadoran courts, Posner said.

In a letter to Posner, a State Department official said the agency regretted the families' decision not to hire a lawyer and said it "will continue to pursue any leads, no matter where they may take us, but that to date, no evidence has come to light which would give credibility to allegations of higher level involvement in this crime."

Posner said yesterday that statements by two Salvadoran national guardsmen in interviews with U.S. officials and law enforcement officers suggested that a superior of the five accused men participated in a cover-up of the murders, at least in the early stages of investigation.