Two weeks before their son is scheduled to be sentenced for espionage, the parents of Ronald L. Humphrey are circulating a plea for leniency on Capitol Hill in which Humphrey states, "Quite simply, I do not have the guts to be a spy."

In a three-page letter to members of Congress describing himself as an "histroical freak" and "a guinea pig," the former U.S. Information Agency employe said he seeks a sentence that "would not selectively punish me for being an accidental, one-of-a-kind victim in a unique legislative and political circumstance."

At a hearing yesterday in Alexandria attended by Humphrey's parents. U.S. District Court Judge Albert V. Bryan Jr. denied post-trial motions by defense lawyers for acquittal or a new trial for Humphrey and his codefendent, Vietnamese expatriate David Truong. Bryan set sentencing for July 7.

Both men face maximum sentences of life imprisonment plus 35 years.

The two men face maximum sentences of life imprisonment plus 35 years.

The two men were convicted on May 19 of funneling classified U.S. diplomatic documents to the Communist Vietnamese in Paris. Humphrey testified that he took the documents from his government office and gave them to Truong, a Capitol Hill lobbyist, without knowing that Truong might have been a spy.

Truong testified that he passed the documents to Vietnamese friends in Paris for use in a peace newsletter.

Humphrey's mother yesterday expressed hope that her son's penalty won't be too harsh.

In his letter. Humphrey sought support for a sentence that "would be relevant to the wrongdoing to which I confessed, namely the leading of confidential [lowest classification] materials for use by another person who was lobbying Congressmen, academicians and the media."

Humphrey said that because the case involved the first test of the president's power to authorize electronic surveillance without a warrant, he was being used as "a guinea pig." President Carter personally authorized the installation of two cameras in Humphrey's USIA office in May 1977.

"I am left as the only American citizen victimized in this manner and subsequently brought to trial," Humphrey's letter continued. "I am not a historical freak."

Humphrey and Troug have been held in the Alexandria city jail since their conviction. The woman Humphrey calls his common-law Vietnamese wife, Kim, and his legal wife, Marylou, also were in the room.