A draft constitution, four years in the writing and nearly two more years under study, is to be placed before President Augusto Pinochet Tuesday, but there are considerable doubts that it will get any further.

Gen. Pinochet promised two years ago that the document would be put to a plebiscite but many political observers, both those supporting and those opposing the military junta that has ruled almost seven years, expect no substantive action by the president.

As several of South America's right-wing military regimes have moved toward the return of popularly elected rule, Chile and neighboring Argentina remain determined holdouts. The impending presentation of the authoritarian draft constitution, however, has offered Chile's traditionally intense politics a slight opening. Debate is under way.

The prospect for a consensus is far from bright. The only opposition groups allowed to express an opinion have already announced they will accept no new constitution unless it is written "by the people" through a freely elected constitutional assembly, similar to that which drafted the new Peruvian constitution and paved the way for free national elections there two months ago.

Pinochet's hand-picked Council of State, headed by conservative former president Jorge Alessandri and consisting of pro-junta civilian and military men, has ended its nearly two-year evaluation of the work of an equally conservative constitutional commission. Now Pinochet will be able to modify it or put it aside.

By all accounts, the yet unpublished final draft would centralize power in the hands of the president, limit the powers of a proposed congress, insure permanent participation of the armed forces in the newly established and powerful National Security Council and give the government wide internal security perogatives.

It would continue to outlaw all "totalitarian" thought and political activity, the device for precluding participation of parties that backed the Marxist government of Salvador Allende, ousted by the military in 1973.

The Chilean constitution of 1925, long considered a modest document of liberal political thought on this continent, was thrown out as the military ended half a century of uninterrupted civilian rule.

In spite of growing opposition to his essentially one-man rule, Pinochet either under enactment of the new constitution or a "transitional statute" would be assured of at least five and possibly 11 more years in power.

But even a draft so amenable to Pinochet's plans may not be acceptable to him. "The document will never come to a plebiscite," said Manuel Sanhueza, head of the opposition Group of 24, which also has been studying the draft and making counterproposals to those of the Council of State.

Sanhueza recently was fired from his post in the law school of a state university, where he had taught for 30 years, because of participation in the opposition group. Though called the Group of 24, it is made up of some 3,000 legal and constitutional specialists and proscribed labor and political leaders.

Sanhueza calls it a Pinochet constitution, "totally dictatorial" and says Pinochet will not allow it to be fully debated and voted on. "To a dictator, a constitution is simply not convenient," he said.

Juan de Dios Carmons, a member of the drafting commission and a central figure on the Council of State, defended the document as "essentially democratic." A one-time minister in the Christian Democratic government of Eduardo Frei, Carmona said a transition period of "five years or so" is necessary to insure the "proper interpretation" of the new constitution.

Carmona said he "hopes" for a plebiscite late this year or early next. He confirmed that the council will recommend that Pinochet name members of a transitional congress to oversee the process.

"Chile has always aspired for a strong, presidential regime," said Carmona, adding that the document will guarantee, above all else, "security, lack of violence, stability and peace."

The proposed constitution would allow for a French-type presidential election, where if no single candidate received an absolute majority of votes, there would be a second round of voting for the two front-runners.

Forces on the right are openly asking Pinochet to shelve the whole affair for at least two more years. Pablo Rodriguez, former head of the extremist Fatherland and Liberty grouping, said any public debate on the issue is "extremely dangerous." "Politically, we are in the exact same situation we were in seven years ago," he recently wrote.

Those who are pushing for a liberalization of the regime hope that the passage into a period of transition can be achieved by some formal vote or the draft. But if there is a national plebiscite, opponents fear it will be similar to one in 1978 prompted by criticism at the United Nations of the Pinochet human rights record.

The vote then was 3-1 in favor of Pinochet, who posed this issue to the electorate: "Faced with the international aggression unleashed against our government, I support the President in his defense of the dignity of Chile . . ." Among those calling the plebiscite unfair was the U.S. State Department.

What Pinochet does in the coming days with the constitutional draft will help determine whether the promise the junta made on Sept. 11, 1973, to return Chile to "order and constitutional rule," will be met. Order has been achieved, but it appears that true constitutional rule will be far more difficult to achieve.