The ruling Sandinista front plans few changes in policy or personnel following its election sweep last month, and there are signs that it will use the victory to justify tougher policies against the conservative civilian opposition, according to Sandinista officials, opposition leaders and diplomats here.

The inauguration of Daniel Ortega as president on Jan. 10 and the swearing-in of a new constituent National Assembly will change the form but is not expected to affect the substance of Sandinista government. The switch from a junta-led to a presidential system is unlikely to diminish the Sandinista front's dominance of the state's administrative apparatus, the sources said.

"We don't expect any dramatic changes because of having an elected government," said Luis Carrion, deputy interior minister and a member of the front's nine-member National Directorate.

Such a course appears likely to draw continued hostility from the U.S. government, which has defended its military, economic and diplomatic pressure against the Sandinistas as partly designed to encourage moves toward western-style democracy here. Washington charges that Nicaragua is following a Cuban or Soviet model, while the Sandinistas assert that they are creating their own.

The front, which has governed since leading the 1979 revolution against Anastasio Somoza, said the election victory had legitimized its rule. Ortega and other senior leaders said the front would carry out its program just as any other party would do.

Making good on a promise to hold elections by the end of 1985, the Sandinistas won 67 percent of the vote against six opposition parties in orderly balloting. Three parties -- considered more conservative than the Sandinistas but sympathetic to them -- placed second, third and fourth for a combined total of 29 percent. Three Marxist-Leninist groups competed feebly to avoid placing last and together received 4 percent.

The turnout was 75 percent, despite a Sandinista voting-day claim of 80 percent. None of the participating opposition parties challenged the results, election officials said.

Nevertheless, a boycott by a sizable share of the opposition, mostly in an umbrella alliance called the Democratic Coordinator, hurt the election's image abroad. The coordinator sat it out on grounds that the government was overly restricting political liberties and that the Sandinistas should hold talks with opposition guerrilla forces fighting along the Honduran and Costa Rican borders.

The coordinator, like the non-Marxist opposition parties that participated in the election, supports enhanced political pluralism and safeguards for private enterprise. It includes four political parties, two antigovernment unions and the national council of businessmen and landowners.

Several opposition leaders who boycotted the election grumbled that the Sandinista-dominated Supreme Electoral Council might have falsified the turnout figures, but they acknowledged that they lacked proof of significant fraud. "We can't prove it in any way," said Dr. Luis Rivas Leiva, who was the Coordinator's president during the election and is president of the opposition Social Democratic Party.

The election left the same individuals heading the government. Ortega, who already is chief of state as coordinator of the ruling three-man junta, will retain that role as president. Another junta member, Sergio Ramirez, was Ortega's running mate on the Sandinista ticket and now is vice president-elect.

"Two-thirds of the junta becomes president and vice president. What change is that?" asked opposition leader Virgilio Godoy, an Independent Liberal. The electoral council kept Godoy's name on the ballot after he had publicly endorsed the boycott. He placed third with 9.6 percent in a presidential contest in which he did not go to the polls.

The third man in the junta, Rafael Cordova Rivas, is to lose his office but remains a prominent leader of the Democratic Conservative Party. Although nominally in opposition, Cordova Rivas is in sympathy with the Sandinistas and has not been known to use his office to oppose their policies.

Some Cabinet changes were expected, but not in the important ministries of Defense, Interior and Agrarian Reform.

In addition, the elections left intact the Sandinistas' control of the national, regional and local government bureaucracies, plus the Army, police, militias and neighborhood block organizations.

One of the opposition's main complaints is the lack of separation between party and state. This is visible daily in traffic patrolmen's round shoulder badges reading "Sandinista Police." State employes and other Sandinista activists accounted for more than half the front's 735,967 valid presidential votes, diplomats and other political observers estimated.

In the legislative branch, Sandinista Carlos Nunez will head the front's majority delegation to the new 96-seat National Assembly. He held a similar role as speaker of the Council of State, the Sandinista-dominated -- and Sandinista-appointed -- legislature of political parties and social organizations that is being replaced by the assembly.

The National Assembly, like its predecessor, is not expected to play a major role in formulating national policy, diplomatic and other political observers said. That responsibility will remain with the front's National Directorate, of which Ortega and Nunez are members.

With 61 seats, the front is three short of the two-thirds majority needed to approve parts of a new constitution that is to be written as the first order of business.

The Democratic Conservatives lead the opposition in the assembly with 14 seats, followed by the Independent Liberals with nine and the Popular Social Christians with six. Each of the three Marxist groupings received two seats.

A high-ranking diplomat and a Roman Catholic churchman, asking that their names be omitted, suggested that the front might use its election victory to justify more radical policies.

There already are indications of such a trend: Press censorship has been tightened, and the government has warned that three political parties in the coordinator might lose some organizing rights after the inauguration, including the right to maintain public party headquarters. Interior Ministry migration authorities recently prevented about 25 opposition leaders from leaving the country for several weeks, citing assorted visa problems in an apparent harassment campaign.

Some opposition leaders, including Arturo Cruz, who was to have been the coordinator's presidential candidate, have predicted that the changeover to a more traditional government system would lead the Sandinistas to ease pressure on the opposition. This has not happened, however, and indications are for the contrary.

Cruz, who lives in a Maryland suburb of Washington, has said he will continue living outside Nicaragua unless the government allows greater liberty of dissent. Pedro Joaquin Chamorro, who recently gave up his title as coeditor of the sole opposition daily newspaper, La Prensa, is moving to Costa Rica after making similar complaints.

The diplomat predicted a harder policy because, he said, socialist states typically respond that way following a period of political "opening" such as the three-month election campaign. Press censorship was relaxed then, and some liberties were granted to opposition parties, including the right to hold public meetings.

The church source, who is pro-Sandinista, said that the front's leadership had given up on what he called the "social democratic" alternative. Now the choice is between Marxism-Leninism and a third, still nebulous alternative, he said. This "third way" would preserve Nicaraguan traditional values and some civic pluralism while breaking up much of the private sector and expanding the state's role in the economy.

"This could be considered utopian, but I think you have to consider utopian ideas when new things are happening," the churchman said.

Senior government officials said decisions regarding the degree of political and economic pluralism would be considered according to their "political" consequences. Measures against the civilian political opposition or the private sector could mar the government's image with important aid donors in Western Europe. But Deputy Interior Minister Carrion said that the opposition had to accept what he called "a process of institutionalization."