United States concern about Nicaragua is growing by the day. Anxiety about the volatile Central American state is underscored not only by what US officials see as Nicaragua's drift toward totalitarianism.
It is also underlined by a massive beefing up of its military force, which poses serious strategic risks for the region as a whole.
''Nicaragua is building a military force which by historic Central American standards is just huge,'' says James L. Buckley, undersecretary of state for security assistance, science, and technology. ''The situation is very, very worrying,'' he told a breakfast meeting of reporters Nov. 17.
Mr. Buckley said the Central American nation's armed forces have tripled in size to 45,000 men since the Sandinistas gained power in 1979. Nicaraguan airfields are ''being enlarged'' and ''heavy equipment'' is being moved in, he said.
Among the other disturbing trends to Washington:
* Nicaragua's highly respected Nicaraguan ambassador to the US, Arturo Cruz Porras, stepped down this week - a move seen as evidence the leadership's Marxist tendencies have become so implanted that even people like Mr. Cruz are finding it difficult to remain associated with the government.
* The Sandinista government threatened to shut down La Prensa, an independent newspaper, again this week for printing a ''tendentious'' story. It has shut down La Prensa five times in the last three months.
* Three of Nicaragua's top businessmen languish in jail for signing a letter last month describing the Sandinista rulers as ''Marxist-Leninists'' and stating that the trend of the government ''will only bring more bloodshed and suffering to our people.''
These developments have prompted some observers who at first criticized Secretary of State Alexander M. Haig Jr.'s recent assertion that Nicaragua may be sliding toward totalitarianism to reverse themselves.
Noting that Congress and many Americans have not favored a bigger US role in Central America, Mr. Buckley told reporters that if Nicaragua were converted into ''a strongly armed extension of Cuba and (therefore) of the Soviet Union,'' that ''may well change the perception of the American people.''
El Salvador Defense Minister Jose Guillermo Garcia recently suggested that a naval blockade of Nicaragua would ''neutralize'' the insurgents in El Salvador. Buckley declined to comment on such a possibility.
The arrest and jailing of the three businessmen and the threats against La Prensa have prompted widespread protest from abroad.
An Inter-American Press Association delegation went to Managua, Nicaragua's capital, recently to make the organization's concern about press freedom in Nicaragua ''patently clear to Nicaragua's leaders,'' as one IAPA spokesman termed it.
Observers say the Nicaraguan leadership's handling of the La Prensa case will indicate whether the country is indeed moving toward ''totalitarianism.''
The IAPA feels it has a stake in La Prensa's future since it made vehement protests against ousted dictator Anastasio Somoza Debayle's attacks on the newspaper in the late 1970s.
There is much to suggest that the Sandinistas are being very careful about their handling of La Prensa. Top Nicaraguan leaders apparently do not want to shut down the paper for fear of international protest.
Nevertheless, La Prensa has now clearly become a thorn in the side of Sandinistas. Government officials argue that the paper is often inaccurate and decidedly partisan. They say it is not helping the reconstruction of the country.
These officials note, for example, that the paper played up the arrests of the three businessmen, but did not give much attention to the arrest of a dozen top Communist Party leaders for complaining that the government has surrendered to capitalism.
Mr. Cruz had long been sympathetic with the Sandinista cause to oust the Somoza government. He was head of the Nicaragua Central Bank after the Sandinistas seized power, then was briefly a member of the governing junta, and finally was made ambassador to the US heal the US-Nicaraguan breach.
Though well liked in Washington, he did not make much headway. He grew dismayed by developments in Nicaragua. His resignation statement indicated his frustration: ''I do not have the means to be able to normalize . . . relations (between the two countries).''
He added, however, that he supports ''the revolutionary process,'' although admitting he was considered a ''dissident.''