Without rejecting them, the British government said tonight that new Argentine proposals made to Secretary of State Alexander M. Haig Jr. for a settlement of the Falkland Islands crisis appeared to fall short of what would be acceptable to Parliament here.

In a statement shortly before midnight near the end of an emergency meeting of senior government officials, a spokesman for Prime Minister Margaret Thatcher said the proposals "are complex and difficult, and at first sight they do not meet the requirements strongly expressed by Parliament, particularly on the need to regard as paramount the wishes of the Falkland Islanders.

"We shall study them carefully, however," the spokesman said, "and shall be getting in touch again with Mr. Haig."

Thatcher received the proposals, which British sources described as "very different" from Argentina's earlier negotiating position, in a message from Haig at about 9 p.m. London time, just as he was leaving Buenos Aires for Washington. British officials said they did not know if Haig would later return to London, a decision that appears to hinge on the initial response he receives from Thatcher.

At tonight's meeting with senior civilian and military aides, Thatcher discussed what answer to give Haig and what recommendations to make to a special Cabinet meeting on Tuesday. Cecil Parkinson, chairman of Thatcher's Conservative Party, joined the meeting to advise her on the likely reaction of Conservative members of Parliament.

Many of them have warned that it could be politically disastrous for Thatcher to agree to joint administration of the Falklands with Argentina under the flags of both countries following a withdrawal of Argentine forces from the islands, as the Argentine military government has reportedly proposed. There also appeared to be no mechanism in the reported Argentine proposals for involvement of the Falklands' 1,800 English-speaking residents in United Nations-supervised negotiations of the future sovereignty and administration of the islands.

Earlier during Haig's shuttle diplomacy, Thatcher's government considered sharing interim administration of the Falklands with the United States or an international body. But Argentine participation in any such administration has been opposed by many members of Parliament. Thatcher also has insisted, with strong parliamentary support, that any negotiated settlement on the Falklands' long-term future be acceptable to the islands' residents.

A number of senior Conservatives said before tonight's developments that giving in to Argentina on these points, even under U.S. pressure, would be considered "too much of a climb-down" by many Conservative backbenchers, particularly those on the party's right wing who have been Thatcher's power base.

"In any acceptable solution," said a senior Conservative with frequent access to Thatcher, "the Argentineans must get out and be kept out until the Falkland Islanders exercise their right to choose."

A Cabinet minister said an acceptable form of participation for Argentina, along with Britain and the United States or other countries in an interim administration, might be built on recognition of Argentina's proximity to the Falklands and its increasing involvement through past agreements with Britain in the islands' communications, transportation and economy. But he ruled out the flying of the Argentine flag or anything like joint Argentine-British policing of the island.

"If Britain gives too much ground," he said, "people would be able to say that aggression does pay."

If the United States forced Britain into "a disastrous climb-down" or failed to back Britain unequivocally if Haig's shuttle diplomacy fails, another minister said, it would risk a great deterioration in support here for the NATO alliance.

British sources had earlier acknowledged that the recent emphasis here on the future of the Falklands' residents, rather than the islands themselves, represents rhetorical movement for the government since the April 2 invasion. Thatcher and her ministers first demanded restoration of British sovereignty, then British administration, and now--in the most recent words used by Foreign Secretary Francis Pym--British "trusteeship" of the islanders' right to self-determination.

Both Thatcher and Pym have suggested that, after the trauma of occupation, the Falklanders might be ready for a change of status.

Adding still more ships and men to the task force, the Defense Ministry announced that 900 paratroopers plus supporting artillery and engineers would depart this week.