International observers, including one designated by representatives of the Democratic Party, plan to monitor Guatemalan general elections Sunday in an unusual effort to assure fair voting in the Central American nation.

A spokesman for Rep. Donald M. Fraser (D-Minn.) said yesterday that Fraser and Rep. Millicent Fenwick (R-N.J.) initiated the effort to have Western democratic parties join the monitoring effort.

Participating along with the Democrats are the international groupings of Christian Democratic and Liberal parties. They will send three observers to insure against fraud that frequently has been alleged in past Guatemalan elections. The Socialist International is expected to send its own monitor.

Prof. John Plank of the University of Connecticut is the observer designated by the Democrats to represent the party.

Such an active role by designates of a U.S. party and of congressmen has no apparent precedent. Last March, a House subcommittee chaired by Fraser held hearings into charges of fraud in Salvadorian elections the previous month.

"But the El Salvador hearings came after the event," said John Salzberg of the House International Relations Committee staff. "This time were trying to do something beforehand."

Heknan Hurtado of the Guatemalan embassy said his goverment has been consulted on the plan to send the observers. "There won't be any problem. We will be glad to have them there," he said, noting that they had requested interviews with the candidates and the minister of interior.

Guatemala is currently ruled by a general and of the three presidential candidates in Sunday's vote, two are generals and one is a colonel. The election of Gen. Kjell Laugeraud four years ago was accompanied by charges of fraud. Laugerud cannot succeed himself.

Leftist opponents of the military contend that the three candidates represent only a small part of Guatemala's 5.7 million population, most of which is Indian and poor.

Long the site of warfare between left-wing and right-wing extremists, Guatemala is widely known as a high-risk area for human rights.

Last month, Amesty International charged that in the final four months of 1977, 113 Guatemalans were killed or abducted by "paramilitary groups . . . characterized by a total impunity before the law."

The Nobel Prize-winning rights group said "there is considerable evidence . . . that abductions and murders, especially of peasant farmers in the countryside, and of slum dwellers and petty criminals in the cities continue unchecked, tacitly condoned at the highest levels of government."

Fraser, Fenwick and 17 other members of Congress wrote Secretary of State Cyrus Vance Feb. 6 citing human rights concerns and "past serious allegations of fraud" in Guatemalan elections and asking that the government there be made aware of U.S. concern.

The letter also asked that Vance endorse the use of international observers. Vance's reply, expected today, is not thought to commit the United States on the observer's question.

Rep. Fenwich, who failed to receive the overall endorsement of the Republican Pary for the effort, has designated one of the three observers as her personal representative.

He is John Richardson Jr. of Freedom House, a New York-based rights group. The third observer Siegbert Alber of the West German Christian Democratic Union.

If no candidate in Sunday's three-way presidential race wins a majority, the presently sitting congress must choose between the two top vote getters.

The candidates include: Gen. Romeo Lucas, 52, backed by the moderate Revolutionary and Institutional Democratic parties; Gen. Ricardo Peralt Mendez, who headed a government that seized power in a coup in 1966.

President Laugerud has not backed any of the three and the outcome is viewed as uncertain, with voter interest low. Also to be elected are 55 congressmen and 425 mayors.