Voice of America chief James B. Conkling yesterday defended his appointment of a senior official who describes VOA as "a propaganda agency," saying that the man is a valuable "creative writer" and simply was expressing "a private assessment" that the broadcasting service adamantly rejects.

There can be no question, the Reagan administration's new VOA director said at a press conference, that the Voice will comply with its legislative charter to be a "reliable and authoritative source of news" that provides "a balanced and comprehensive picture of America."

Conkling sought to quell dismay among many of the agency's professionals over the disclosure that Philip Nicolaides, the new deputy program director for commentary and news analysis, urged Conkling to abandon the "tendency toward mush" and engage in hard-hitting "propaganda."

A petition was circulated among VOA employes yesterday urging Conkling to cancel the Nicolaides appointment because his concepts would "destroy our credibility and ultimately the organization itself." The petition, referring to a report in The Washington Post Friday, said Nicolaides' plan "to turn VOA into a blatant propaganda tool is an outrage."

Conkling was quoted in the same news account as disavowing the Nicolaides plan. Meeting with the agency's employes yesterday afternoon, and later with the press, Conkling said neither he nor Charles Z. Wick, director of VOA's parent organization, the International Communication Agency, has any intention of adopting the recommendations made by Nicolaides in a Sept. 2l memorandum to Conkling.

Both men took oaths, Conkling said, to honor VOA's charter and are determined that the agency will remain a "non-politicized, non-propaganda, highly professional" organization.

Among the agency's 2,200 employes, Conkling said, "we have a large share of Democrats, a large share of Republicans, a large share of liberals, a large share of conservatives, and a large share of non-committed people. That is fine as long as they don't bring it to work with them. When they write, when they articulate, it has to be exactly non-political. They cannot write with prejudice; they cannot speak with prejudice."

Nicolaides is a former radio commentator for KLYX-FM in Houston, who has worked in the campaigns of several prominent conservative politicians. When he asked, as a new ICA employe, to work for the Voice, Conkling said, he was asked to explain his ideas. The Sept. 21 memorandum was the result, Conkling said, and it contained "some excellent ideas" and "some fascinating points," and also "some very unattractive ideas from the standpoint of the Voice of America."

Conkling said he rejected the bulk of Nicolaides' ideas that have been reported, and hired Nicolaides, instead, to concentrate on what he believes "should be more upbeat" about America in VOA broadcasts, because Nicolaides is "an excellent writer" who can help inject "a little more vigor," drama and "excitement" into Voice broadcasts. Nicolaides will not have the final word on any Voice policy, Conkling said, as there will be four layers of higher-ranking officials above him.

The idea that there might "a whiff of McCarthyism" in the agency, Conkling said, appalls him. "The word 'McCarthyism,' " Conkling said in the VOA auditorium, "is the worst word that can be heard in this room."

Conkling said that despite the comments by Nicolaides, and his comparison of VOA's function to a salesman selling soap or other products, "I consider him innocent" of any prejudice that can affect his job at VOA, until there is evidence to the contrary.

In a farewell memorandum circulated to the VOA staff, M. William Haratunian, who was replaced last week as Conkling's deputy, said the question is whether the new political leadership of the Voice will trust its professional staff "to make impartial and journalistically competent editorial decisions." Haratunian, awaiting reassignment, said he is "deeply troubled" by recent personnel actions" which he said are "being perceived as punitive," which "in turn tarnishes the reputation of VOA."