Delilah Yoder, a 27-year-old Arlington social worker, traveled with a friend to Central and South America in early 1976 and planned to talk to witch doctors on Ecuador about medicinal herbs that were said to cure terminally ill cancer patients.

Somehow, somewhere in the vast Amazon jungle of Ecuador during May of last year, Yoder and her friend, computer analyst James Herschberger of New York, mysteriously disappeared.

More than a year later, after spending $50,000 to try to determine what happened to Yoder, her seven brothers and sisters say they still have no answers.

Part of the reason they have been unsuccessful in their efforts to find Yoder and Herschberger, her relatives bitterly complain, has been the lack of cooperation from U.S. State Department officials.

David H, Yoder, a real estate developer in West Virginia and Miss Yoder's older brother, told a House International Relations Subcommittee on International Operations this week that the family's efforts to find the two people have been "severely hindered by the ineffective and unresponsive attitude of the State Department."

The Yoder family gave to commitee members a lengthy statement of their attempts to find their sister and how they said they had been stymied by the State Department.

The table of contents of report points to what they said they have encountered from the U.S. government - "Refusal to Act," "Lack of Initiative," "Lack of Coordination," "Lack of Responsibility," "Lack of itelligence Information," "Discrepancies and Misrepresentations," and "Obstructions to the Investigation."

Yoder said that an Ecuadorean named Marcelo Carrion apparently was the last person to see Yoder and Herschberger.

"He (Carrion) asked them to his jungle farm, and from that point, they disappeared," Yoder said his sister's last letter to the family was written May 11 of last year. She said in the letter that on May 14, she and Herschberger were travelling east of the Andes to Carrion's jungle farm to talk to the Indian doctors.

Yoder said he has no substantial information about what has happened to his sister, even though the family has hired investigators from an international organization to help them.

Both the Yoders and State Department officials report that Carrion had given several conflicting accounts of where Yoder and Herschberger were going when they left the Amazon jungle - if they ever left.

The House subcommittee held heavyings Tuesday and yesterday investigating complaints that Americans abroad do not receive prompt and effective help from the U.S. government. Subcommittee members heard testimony about American prisoners in Boliva and the deaths of Americans in Chile, as well as the disappearances in Ecuador.

Sobcommittee Chairman Dante B. Fascell (D-Fla.) said in an opening statement yesterday. "While I recognize the tremendous devotion to duty and outstanding work performed by our consular officials, I am personally appalled at the apparent lack of sensitivity, timely attention and follow through demonstrated in many of the cases brought to our attention.

The subcommittee conducted the hearing at the request of Rep. Jerome A. Ambro (D-N.Y.), who has investigated the disappearance abroad of several Americans while trying to find the missing daughter of one of his constituents.

Barbara M. Watson, administrator of the State Department's Bureau of Security and Consular Affairs, told the subcommittee, "I want to emphasize that we know we are not perfect, but given your present mandate and our existing resources the Counsular Service is doing a dedicated, creditable job." She added that the office is confronted with "a revolution of rising expectation."

Watson said that more than 1.3 million Americans live abroad, and 7.5 million probably will travel to foreign countries this year.

Concerning the disappearance in Ecuador of Yoder, Herschberger, and a woman from New York, a State Department official told committee members that his department, the U.S. Embassy at Quito, Ecuador, and others "have attempted throughout to be helpful and sympathetic to the families in the United States."

The official, William P. Stedman Jr., deputy assistant secretary for inter-American affairs, added that the Ecuadorean authorities have the responsibility for investigating the disappearances.

The Yoders said they asked the State Department to release any vital information they may have concerning their sister's disappearance. State Department officials yesterday assured subcommittee members that they will do so "shortly."

A State Department spokeswoman estimated that there are 15 Americans who are listed as having disappeared in various countries, including Mexico, the Philippines, Ecuador and in Europe.

She said about 2,200 American are imprisoned abroad, about 75 per cent of them arrested on narcotics-related charges.