Retired admiral Daniel J. Murphy, Vice President Bush's former chief of staff, advised Panamanian military leader Gen. Manuel Antonio Noriega last November about how to improve his damaged political credibility, according to a former top aide to Noriega and a State Department official.

Because of Murphy's close administration ties, Noriega interpreted the discussion as a sign that Noriega still had White House support, according to U.S. officials and Panamanian opposition sources. Murphy said he was in Panama on private business.

The ties also caused the opposition leaders to question whether the administration was backing away from its demand that Noriega step down as de facto ruler, the sources said.

While there is confusion about precisely what Murphy said to Noriega, a State Department official confirmed this week that Murphy's visit was a factor in the administration's decision to send Richard L. Armitage, assistant secretary of defense for international security, to meet with Noriega late last month.

Armitage was instructed to reiterate to Noriega that the administration wants him to resign and allow free elections in Panama, officials said.

U.S. officials said Murphy was speaking as a private businessman, not a representative of the administration or as an emissary from Bush. Murphy has been in the international consulting business since he left Bush's staff in 1985.

U.S. relations with Panama have deteriorated sharply since intense anti-Noriega rioting there last summer, which gave rise to the most sustained opposition against him. Administration officials have stepped up efforts to persuade him to resign, and Congress has voted to end aid to Panama, except for humanitarian and disaster relief.

State Department and congressional officials said Murphy's visit provides the latest example of Noriega's repeated attempts to exploit for his political benefit meetings with ranking former and current administration officials.

A State Department official said that Murphy, as a private businessman, was free to discuss whatever he wanted with Noriega, but that the visit probably complicated the administration 's efforts to have him step down. "Maybe it's not something we would have wanted to happen," the official said of the visit.

Murphy's stature also was enhanced by his ability to draw on his past administration ties and to arrange meetings in connection with his Panama trip with Lt. Gen. Colin L. Powell, President Reagan's national security adviser; Elliott Abrams, assistant secretary of state for Latin America; and Donald Gregg, Bush's national security adviser.

Murphy said last night that he was asked by a group of American businessmen interested in restoring stability in Panama to explore the possibility of representing them or the Panamanian government.

Declining to be more specific about his conversation with Noriega, Murphy said he discussed U.S. policy toward Panama and tried to see if Noriega was flexible about political improvements.

"I was really trying to find out whether there was negotiating room between him and the opposition," Murphy said. "I did nothing against what the U.S. policy was . . . . "

Murphy said that he has not decided what further role, if any, he might play and that he would not become involved with Panama if it counters U.S. policy.

Jose I. Blandon, a close adviser to Noriega until the general fired him last week as consul general in New York, said "the problem with this Murphy mission is that he left the impression in Panama that some members of the administration support Noriega."

Blandon said Noriega told him that Murphy said Noriega could stay in office through early 1989, if he allowed political reforms, including free elections and an unhampered opposition press.

A State Department official with direct knowledge of a meeting between Abrams and Murphy after the visit to Noriega, said Murphy told Abrams that he made political recommendations to Noriega. Murphy said he discussed the election issue but did not tell Noriega that could stay in office through early 1989, pending reforms.

Blandon has played a leading role in an effort to negotiate, initially with Noriega's approval, a political settlement that would allow transition within a year to full civilian government and Noriega's retirement in April. However, Noriega abruptly ordered Blandon to halt his efforts late last month, fired him last week and publicly branded him a traitor.

According to reports within the Panamanian opposition and Blandon statements, Murphy's meeting with Noriega was allegedly part of a larger effort to improve Noriega's image and involves two politically well-connected Washington lobbyists, Thomas Hale Boggs Jr. and William E. Timmons, and South Korean businessman Tongsun Park.

Boggs said yesterday that he, Timmons, Park and Murphy are not working together to help Noriega. Park was the leading figure 10 years ago in a Washington influence-peddling scandal involving payoffs to members of Congress.

"Tongsun is involved with the businessmen who contacted me," Murphy said. "He appears to have long-term business interests in Panama . . . . He came to me as an international businessman." During his meeting with Noriega, Murphy said, Park "was in and out a couple of times."

Boggs, a Democratic Party fund-raiser, is the son of the late House majority leader. Boggs said he, Park and Timmons, a prominent Republican, have been friends since they attended Georgetown University. He said he does not believe that Timmons is involved in business deals in Panama. Timmons declined to be interviewed.

Boggs said that, at Park's request, he met with Noriega in Panama last winter and offered advice on how to improve his image here. He said that Noriega was seeking a Washington representative but that his firm decided against doing business in Panama.