Britain and Argentina, despite significant changes in their negotiating positions, appear to remain far apart on many points of contention in the Falkland Islands crisis.

There are signs here and in Buenos Aires that the large gaps between the two countries can be bridged only by compromises that would involve great political risk for both British Prime Minister Margaret Thatcher and Argentine President Leopoldo Galtieri.

The two sides appear irreconcilable on what for the Argentines is the crucial question: whether Argentina, if it first withdraws its forces from the Falklands, would be assured of eventually gaining uncontested sovereignty over the islands regardless of the wishes of the 1,800 English-speaking inhabitants.

To resolve this impasse--even by a compromise like a United Nations trusteeship of the islands, which would appear to be unacceptable to Argentina--Thatcher would have to back away from self-determination for the islanders. But she has made this extremely difficult politically by repeatedly making it her most important point of principle in public statements on the crisis.

There is clear concern in Buenos Aires, reports Washington Post correspondent Jackson Diehl, that no matter how much ground Argentina gives on other issues, it may be impossible to win agreement on the sovereignty question.

Some analysts in Buenos Aires believe Galtieri already may have reached the limit of the Argentine military's tolerance for compromising what it sees as the great victory it won in seizing the Falklands three weeks ago. Doubts have even been raised here about whether Galtieri will be allowed to carry out the concessions that Argentina's military junta agreed to earlier this week in marathon talks with U.S. Secretary of State Alexander M. Haig Jr.

Throughout the crisis, the British appear to have remained firm on three points. Argentina has agreed in principle to the first, a withdrawal of its forces from the Falklands so long as Britain pulls back its naval task force, whose vanguard is now only a day or two from the islands. There appear to remain significant disagreements over how the withdrawal would be carried out and its linkage to other parts of a peace agreement.

Thatcher's second objective, restoration of British administration of the islands, appears open to some form of face-saving compromise. But there is a wide gap between Argentina's latest proposal for a shared transitional administration under U.S. supervision and British insistence on the return, at least temporarily, of unilateral British rule.

A British source says Thatcher may be willing to approve some sort of international role that would include Argentina in helping administer the islands "to give Galtieri a ladder to climb down."

Finally, Thatcher has continued to insist on her third point--that the wishes of the islanders must be the "paramount" consideration in sovereignty negotiations following the peace settlement. The Argentines believe a veto for the islanders over any settlement could deprive Galtieri's government of eventual control of the Falklands.

Tension over these remaining points of dispute is increasing here with the expectation that Britain's Falklands task force will take some sort of military action next week if significant progress is not made. Expressing a widely held view among members of Parliament, Conservative lawmaker Jonathan Aitken said, "A shooting war is still an odds-on certainty. I don't think the British government can compromise very far, and the junta is not speaking with one coherent voice."

The contents of the new written Argentine and British proposals submitted to Haig have been kept secret, although there have been reports in the Argentine media described by officials here as "edited leaks" for propaganda purposes.

After seizing the Falklands on April 2, Galtieri refused to withdraw his troops unless Argentine sovereignty over the islands was immediately recognized. The most Argentina was willing to concede to the British at first was good treatment for the Falklands' residents, the opportunity for them to leave or retain British citizenship and possible British participation in economic development of the islands.

Backed by a U.N. Security Council resolution, Britain demanded an immediate and unconditional Argentine withdrawal and the restoration of British rule before any negotiations could begin.

During Haig's shuttle diplomacy, the British, nevertheless, allowed themselves to be drawn into comprehensive, detailed negotiations. According to well-informed sources here, the British also considered international involvement in a post-withdrawal interim administration of the islands, although apparently without Argentine involvement. The British also appear ready to agree to a time limit for negotiations over long-term sovereignty.

Fearing sovereignty talks would again drag on as they had since 1965 before the invasion, Argentina has proposed a deadline of Dec. 31, sources said.

The Argentine government, meanwhile, moved from its original position to a willingness to accept a joint interim administration of the islands with Britain and drop its demand for immediate recognition of Argentine sovereignty, so long as the negotiating mechanism assured an eventual transfer of sovereignty from Britain.

But the complex proposals that Argentina made to Haig, which ran to several pages in the form transmitted to London, contained what one British source called "a minefield" of problems for Thatcher. Another source said they were "full of gremlins."

Among these apparently were arrangements for a joint transitional administration. Argentina proposed that the islands be run during an interim period by a council containing Argentine, British and islander representatives, and that they be policed by Argentine and British officers. Under the proposal, the flags of all three countries would fly over the island, with the U.S. establishing a mission on the Falklands to guarantee and supervise the settlement process.

Many Conservative lawmakers and some from other political parties oppose any Argentine share in administering the islands as "rewarding Argentina for its aggression." An Argentine police presence in the islands would also be seen as a symbolic continuation of the military occupation.

Argentina also appears to have proposed an unusual process for negotiating future sovereignty in its favor, possibly under United Nations auspices, based on the United Nations' decolonization policy.

Britain has given independence to dozens of its former colonies since World War II, but always based on local self-determination. The Argentine peace proposals reportedly envision the United States as guarantor to guard against the islands becoming independent.

The British government has been ready in past negotiations to grant Argentina sovereignty over the Falklands. But it also has committed itself to respecting the wishes of the islands' residents, who have always opposed any change in their relationship with Britain.

Any move by Thatcher away from this commitment would be bitterly opposed by many in Parliament, particularly by right-wing Conservatives who have been the prime minister's power base. Depending on whether Argentine and Britain are willing to compromise on numerous other points of contention, this is increasingly seen here as the ultimate hard choice facing Thatcher if war with Argentina is to be avoided.