In its boldest gamble to reach a Rhodesian peace settlement, the British government today moved to push the warring parties to reach a final agreement on a ceasefire by sending a senior official to take power in Salisbury.

Upon his arrival Wednesday, Lord Soames will take complete control of the government as British governor, immediately restoring the British colony to legality for the first time in 14 years and ending British economic sanctions.

In Salisbury, the short-lived unrecognized government of Zimbabwe-Rhodesia ceased to exist tonight as Parliament voted to dissolve itself, Washington Post Correspondent Jay Ross reported.

The 90-to-0 vote symbolized the end of the unilateral declaration of independence proclaimed in 1965 by then prime minister Ian Smith as a way to maintain white-minority rule.

Surprised Labor Opposition members in London's House of Commons immediately questioned the British move when Prime Minister Margaret Thatcher and Foreign Secretary Lord Carrington disclosed Soames' imminent departure just minutes before he boarded a plane for Salisbury.

Opposition leader and former prime minister James Callaghan immediately voiced "serious reservations" about Soames' depature. Peter Shore, Labor spokesman on foreign affairs, said, "to throw him in there before the cease-fire has been agreed is a foolish policy and a foolish act."

There was no official Patriotic Front reaction to today's development but informal comments were noncommital and suggested no hostility toward the British move, which was accompanied by British proposals to assure the safety of guerrilla forces.

Soames, who is accompanied by his military adviser, Maj. Gen. John Acland and 45 British officials, will assume command of the Salisbury government's military forces who have been fighting Patriotic Front guerrillas for the past seven years.

Underlying the risky gamble is Britain's effort to bring an end to 14 weeks of peace negotiations here by forcing the Patriotic Front leaders to agree on details for implementing the British cease-fire plan and sign a final peace agreement as soon as possible.

The British also want to stop armed guerrillas from infiltrating into Zimbabwe-Rhodesia from bases in neighboring African countries and prevent the Salisbury force from retaliating with attacks on those bases in Zambia and Mozambique, as they did in bombing raids again on Sunday. Britain feared this escalation of the war would unravel agreement already reached at the peace talks here.

Because the Salisbury government and its military have agreed to transfer power to Soames tomorrow, he could order an end to the retaliatory raids, as British officials today hinted he would. But he will have no authority over the Patriotic Front guerrillas under their leaders agree here to sign a cease-fire.

Until then, the Salisbury forces would, from Wednesday on, be fighting the guerrillas under British government authority. If the Patriotic Front ultimately fails to agree to a cease-fire, Soames could be left to carry out the British plan for elections and legal independence in the midst of a continuous war.

"From tomorrow," said Patriotic Front spokesman Eddison Zvobgo, "any killing done by the Rhodesian regime will be the responsibility of the British governor."

British officials said they still hoped the final peace agreement could be signed this week. Carrington gave the Patriotic Front leaders today detailed British explanations of the implementation of the cease-fire that he said "should allay the fears" about the safety of their forces.

While the guerrillas are to be gathered into 14 assembly places so that their maintenance of the cease-fire can be monitored, the Salisbury forces would be similarly confined to 40 of their bases. British officials said the Salisbury military would use three times as many bases because its forces are three times are large.

"The British government cannot accept that Patriotic Front forces which assemble under the auspices of the monitoring force and which accept the governor's authority and comply with his directions will be in any danger of attack from other forces," Carrington told the guerrilla leaders. "There could, in these circumstances, be no danger to their security."

But Carrington cautioned the Patriotic Front that the Salisbury troops would be confined to their bases only if the guerrilla forces moved into the assembly places from hiding in the bush. Any guerrillas who did not go the assembly places would become illegal forces, subject to whatever action the British governor might order a against them.

Armed guerrillas also would be forbidden from entering Zimbabwe-Rhodesia from neighboring countries after the cease-fire agreement was signed, which is one reason why the Patriotic Front leaders have been drawing out the negotiations here after accepting the British cease-fire plan in principle a week ago. Unarmed Patriotic Front supporters, however, would be helped to return to Zimbabwe-Rhodesia from exile so they could participate in the new election.

Carrington emphasized that the forces of both sides would be monitored in exactly the same way, would retain their arms and equipment, and would be under the direction of their commanders, subject to the ultimate authority of the British governor.

Carrington explained that "the Patriotic Front forces will be sited in their [present] operational areas in locations which will meet their concern that they should not be in close proximity to Rhodesian bases."

The British gave both delegations maps of Zimbabwe-Rodesia pinpointing the Salisbury forces' bases, concentrated around Salisbury and along the northern and southern borders, and the guerrilla assembly places, scattered in more distant, rural areas that the Patriotic Front claims to control.

"The contacts we have had over the past week," with Patriotic Front leaders, Carrington said today, "really do lead me to believe that the proposals we have put forward should allay the fears of the Patriotic Front and we should therefore get a quick agreement."