The staff of the Senate Select Committee on Intelligence yesterday began an inquiry into published reports that members of a U.S. Army helicopter outfit secretly had flown missions into Central America. The Defense Department strongly denied the reports.

Knight-Ridder Newspapers distributed weekend articles quoting relatives of dead Army helicopter crew members as saying the men, dressed in civilian clothes, flew at night to help pro-American forces in Central America.

The crew members were told, according to Knight-Ridder, that the nature of their missions would not be revealed if they were downed or killed.

They were instructed to blow up their helicopters if they survived crashes, according to reports quoting relatives of 17 pilots of the Army's 160th Task Force at Fort Campbell, Ky., who were killed last year.

The Pentagon's chief spokesman and the Army chief of staff strongly denied the Knight-Ridder accounts when queried by The Washington Post yesterday.

"The 160th has never been in El Salvador, has never been in Honduras, has never been in Nicaragua and has never flown in their airspace," Pentagon spokesman Michael I. Burch said. He said the 17 deaths in 1983 occurred "in the continental United States."

"Absolutely, totally and irrevocably false," Gen. John A. Wickham Jr., Army chief of staff, said when asked about Army pilots engaging in clandestine missions in Central America.

Wickham said the 160th engages in secret activities that could not be discussed. Army sources said the 160th sometimes transports elite antiterrorist Army units on missions.

Sen. Richard G. Lugar (R-Ind.), a member of the intelligence panel and incoming chairman of the Foreign Relations Committee, was among those who read the Knight-Ridder reports and wanted them checked.

He asked the intelligence committee staff to check the reports with the Defense Intelligence Agency and Central Intelligence Agency, a Lugar spokesman said.

House Foreign Affairs Committee Chairman Dante B. Fascell (D-Fla.) and Sen. Carl Levin (D-Mich.), a member of the Armed Services Committee, also asked that the reports be checked to determine if the Reagan administration has violated restrictions on U.S. aid to the so-called "contras" fighting the Nicaraguan government.