Amid mounting coup rumors, Guatemalan President Efrain Rios Montt decreed a "state of alarm" and dismissed six key officers from his government today after a cashiered colonel and an underground politician denounced him on local television as a "traitor" and "religious fanatic."

The crackdown brought to the surface a series of accumulating reports that some of the young Army officers who brought Rios Montt to power in a March 1982 coup have become disenchanted with his evangelical rule and are agitating for his removal or resignation. Their dissatisfaction has come alongside, but is not necessarily connected with, growing frustration among politicians awaiting elections that Rios Montt frequently has promised but has never actually scheduled.

The six officers whose resignations were accepted today were officially advisers to the president. Guatemalan and diplomatic sources said they were representatives of the young officers who put Rios Montt in place 15 months ago, meaning their actions in the days to come were likely to have a decisive influence on the future of his government.

None of the officers was heard from after announcement of the decree and their resignations, which Guatemelan sources said amounted to dismissals.

Lt. Col. Angel Arturo Sanchez, the best known of the six resigned officers, was Rios Montt's chief of staff. The announcement of their departure said only that the officers would resume military duties.

The resignations, also included Victor Manuel Argueta Villalta, Mario Rene Enriquez Morales, Carlos Rodolfo Munoz Pilona, Mario Augusto Rivas Garcia and Hector Mauricio Lopez Bonillo.

The streets later today appeared busy and calm. Unconfirmed reports, however, said traffic had been stopped for a time and unusual troop movements were seen around the presidential palace before dawn.

Rumors of a possible coup attempt accelerated when Guatemalan radio stations joined in a national network from 6 a.m. to 9 a.m. and broadcast military music interspersed with appeals for calm. But then they resumed normal broadcasting, only to join in a network again at 11:15 a.m. until the decrees were announced at 4 p.m. by presidential spokesman Gonzalo Asturias.

A Guatemalan legal source said the "state of alarm" differs only technically from the state of siege that had been in effect here until March. It was lifted as part of a opening that Rios Montt said would lead to elections for a constituent assembly some time next year. Under the new measure, as under the old, basic civil rights such as freedom of assembly, movement and speech were suspended.

In announcing the decree, Rios Montt said the new restrictions came in reponse to "frank defiance of public power undertaken by the eternal nonconformists." He pledged they would be temporary.

The defiance came in an extraordinary television appearance late last night by dismissed colonel Luis Francisco Gordillo Martinez, one of the officers who played a part in Rios Montt's rise to power March 23, 1982. Gordillo was fired and briefly imprisoned on charges of talking politics while in uniform several months ago. Last night, he called on Rios Montt to resign and suggested that Guatemalan Army officers may be sworn to protect the nation, but not the president.

His remarks were seen as an indirect invitation for a new military coup, particularly against the background of coup rumors that have been moving through this city with increased intensity during the past two weeks. Rios Montt's removal would open an unknown perspective for the Reagan administration, which recently announced its willingness to sell spare helicopter parts to his government after several years of an arms embargo because of the government's civil rights abuses.

After President Reagan met with Rios Montt in November in San Pedro Sula, Honduras, he said the Guatemalan leader was getting a "bum rap," in the United States and suggested he would soon ask Congress to end the arms sales embargo.

Gordillo, 47, said finance minister Leonardo Figueroa Villate came to him with $50,000 in cash recently and urged him to take the money and leave the country. Gordillo turned down the offer, he declared on the television broadcast, adding that he will now go underground to help lead the opposition.

After several commercials, Gordillo was followed on the screen by Lionel Sisniega Otero, a politician who diplomatic sources said has been in hiding or exile for months. Sisniega called Rios Montt a "traitor" to the March 1982 revolution and the Guatemalan people. He accused the president of being a "religious fanatic" who believes he has received his mandate to govern the country directly from God.

Rios Montt is a born-again Christian who follows the teaching of the evangelical Church of the Word, based in California. He appears most Sunday nights on television to deliver fundamentalist homilies and bases his policies on the same Protestant precepts that he preaches.

Sisniega is a former vice chairman of the National Liberation Movement, an arch-conservative political party that is reputed to be the best organized and strongest in the country. The party has been locked in a struggle with Rios Montt over several issues, including his plans to impose new taxes and the party's demands for early elections.

In spite of the day's events, government officials said a swearing-in ceremony for a new tribunal to regulate elections will go on as planned Thursday.