South Korean protests against the alleged U.S. bugging of the president's mansion subsided yesterday after the U.S. Embassy formally denied that eavesdropping ever took place and expressed regrets that reports of it had inconvenienced the Korean government.

A written statement of denial from Ambassador Richard Sneider apparently satisfied the South Korean government, which had tolerated demonstrations around the embassy for a week with little interference.

Riot police lined the embassy's front entrance yesterday for the first time since demonstrations by war veterans, housewives, war widows, trade unionists and students began last week.

Yesterday, only one demonstration involving about two dozen war veterans was held at the embassy.

The protests are presumed to have government sanction because President Park Chung Hee's emergency decrees prohibit public demonstrations without a government permit.

(Sources in Washington said yesterday that the demonstrations clearly seem to be related to the congressional request for testimony from former South Korean ambassador Kim Dong Jo. House and Senate investigators want to question Kim about allegations that he made cash payments to members of Congress.)

The protests were triggered by a television interview in which former ambassador William Porter made statements implying that a bug had been in the president's home sometime before Porter's arrival here in 1967.

In a CBS News interview broadcast April 3, Porter was asked about reports that American intelligence had bugged the presidential mansion. He replied, "I was told it had stopped before my arrival."

Porter added: "I gave a specific order that it was not to be renewed."

These statements were reported by some media as confirmation of earlier speculation that the U.S. had a "bug" in the South Korean president's home.

(In a telephone interview yesterday, Porter, who is now retired, said the reports that he had confirmed the presence of listening devices were "sloppy journalism." He added; I couldn't have confirmed anything, because nothing like that happened when I was there. I only said that I had been told about it; I don't know if it happened or when it did.")

TR for pickup

A Foreign Ministry spokesman said Sneider's letter to foreign Minister Park Tong Jin denied that the U.S. had conducted electronic eavesdropping operations on the Blue House, President Park's official home, the spokesman said the letter expressed regret that former ambassador Porter's statement had caused an inconvenience.

The text of the message was not released and the U.S. Embassy refused to comment, except to say that the Foreign Ministry's version was correct.

Sneider had orally denied the reports of bugging last week in a meeting with Park Tong Jin, but the South Korean government wanted a formal written assuarance. It received Sneider's letter Friday and released it yesterday.

Allegations of bugging first surfaced in 1976 and have been denied ever since. Last August, Central Intelligence Agency director Stansfield Turner categorically denied that any agency had bugged the house.

The South Korean government publicly accepted that denial and often cited it when new reports surfaced alleging that President Park had held a meeting to plot a widespread lobbying campaign in Congress and that meeting may have been electronically overheard.

Porter's statement in a CBS interview April 3 revived the controversy, apparently prompting the South Korean government to tolerate the series of protests as a means of bringing pressure for more forceful U.S. denials.

"When a former ambassador says we bugged you, what can you do?" said one American official.

U.S. officials were surprised by the force of some of the demonstrations but assumed that they were under government limitations and could be turned off as quickly as they were turned on.

They said the government had deliberately discouraged some protests and had made sure that the student rallies did not get off campus and into the embassy area.

"We did not regard it as a wild spree of emotion," said one official. "I don't think that they [the government] really wanted to let things get out of hand."

Thousands of high school and college students had participated last week. One mass rally of some 1,800 students was held at Seoul National University, normally a center of opposition to President Park's government.

Several rallies were organized by the Federation of Korean Trade Unions, a government - controlled labor movement.

In previous years, antigovernment demonstrations in Seoul have provoked mass arrests and some participants remain in prison for months. In recent months, however, the government has slightly relaxed its tactics and the general practice is to pick up demonstrators in police vans and drop them off in remote sections of the city.