Using a U.S. congressman as an intermediary, PLO leader Yasser Arafat has suggested that outgoing U.N. Ambassador Andrew Young visit him in Beirut, and has been sent a reply that leaves open the possibility of such a meeting sometime after mid-September.

But a spokesman for Young said that the congressman, Rep. Paul Findley (F-Ill.), had not been authorized to convey such a statement to Arafat, adding that he doubted Young would meet with the leader of the Palestine Liberation Organization.

Young's spokesman confirmed, however, that the ambassador and the congressman had talked about Arafat's suggestion. And he confirmed that Young will visit the Middle East in the fall, after he officially leaves his U.N. post.

Young resigned under pressure Aug. 15 after disclosure that he had held an unauthorized meeting with the PLO'S observer at the United Nations and had then misled the State Department about the nature of that meeting.

U.S. policy since 1975 has been that U.S. officials will not negotiate with the PLO because that organization does not recognize Israel's right to exist as defined by U.N. Security Council Resolution 242.

Just after Young's resignation was announced, Findley said in a telephone interview, he received a telephone call from Lebanon from one of Arafat's deputies.

Findley, who has long maintained contact with the PLO and is sympathetic to their cause, said that Arafat's deputy said the PLO leader wanted him to extend his "greetings and best wishes" to Young and to ask if Young is in a position to accept an invitation to visit Arafat in Beirut.

The next day, Young stopped in Findley's Capitol Hill office while making the rounds of a few members of Congress. Findley and Young talked about the message from Arafat. After that meeting Findley sent Arafat a letter in which he purported to convey Young's response to Arafat's suggestion. Findley's letter, dated Aug. 23, said that Young planned to visit the Mideast, including Israel and southern Lebanon, but not until "mid-September, at the very earliest." The letter added:

"He [Young] said, while appreciating very much your generous comments and suggestions, a direct response at this time would be unwise."

This clearly left open the possibility that Young wants to meet with Arafat, and may welcome a formal invitation at a later date. But Young's executive assistant, Stoney Cooks, said that is not the case.

Cooks confirmed that Young had talked with Findley about the message from Arafat. "We said that at some point Andy wanted to go to the Middle East, to Israel, Lebanon, southern Lebanon," Cooks said. "But we said it is in his interest to go at the invitation of the Lebanese government, and not at the invitation of Arafat's office."

Cooks added that he did not think Young would meet with Arafat. "It is not in his interest to meet with Arafat," he said ". . . It would be inflammatory in this country. He is not interested in being Arafat's PR man in the United States."

Cooks said that Young felt it would be "unwise" for Arafat to extend an invitation to Young for a visit "because if Andy received it he'd probably have to reject it."

He added: "Andy has not commisioned Paul Findley to intervene in his behalf or be his emissary . . . . I've never seen this letter or heard of this letter before."

Findley, who is vacationing in New England said in a telephone interview that he passed on to Young the suggestion and best wishes from Arafat because he believes that such a meeting would help promote better understanding in the United States of the Palestinian cause. "I'd like it [the meeting] to occur," he said.

Findley said his latest role as message carrier came about because he to President Carter and had passed them on to the White House. But he said he had never gotten a reply from the White House to Arafat.

Findley said his latest role as message carrier came about because he received a telephone call from Arafat's deputy, Mahmoud Labadi, who was in Beirut, within hours after Young resigned.

In his letter to Arafat, Findley termed Young's resignation an act of "statesmanship," a resignation over "high principle," and he likened it to the resignation of former British prime minister Anthony Eden and Richard M. Nixon's Watergate Saturday Night Massacre victim, Elliot L. Richardson.

Findley's view, as presented to Arafat in the letter, was that Young had "insisted that the president accept his resignation . . . to assure that the result of the controversy will be public discussion of the Palestinian problem . . ."

Findley's letter added that "Lebanon will be included in his [Young's] tour" of the Mideast and that "he will want to visit southern Lebanon." It added, "He feels that his schedule of tours and appointments while in Lebanon should be made through the officials of the Lebanese government."

Young's assistant, Cooks, stressed that Young's Mideast visit will not be made until he is out of office, "probably in mid-October or November."