More than 150,000 supporters welcomed back nationalist leader Bishop Abel Muzorewa home yesterday from his inclusive talks with top British and U.S. officials on the recently concluded internal agreement for solution of Rhodesia's constitutional crisis.

While the crowd was impressive, it fell short of that anticipated by followers of the diminutive bishop - the leading black nationalist based in this breakaway British colony. The turnout left observers wondering whether Muzorewa will be able to sell the internal agreement even to his own people.

The plan calls for establisment of an interim multiracial government later this week, to led by the four signatories - Muzorewa, three other black leaders and Ian Smith, prime minister of the current white minority government. A black majority government is to take over Dec. 31.

Muzorewa's popular support has become a crucial issue following the U.S. Security Council's rejection of the internal accord last week and the refusal of Britain and the United States to come out clearly in support. It is also opposed by exiled black nationalist leaders.

The bishop's United African National Council had made a big effort to organize the most massive welcome ever accorded a returning Rhodesian politican and predicted that over half a million of Rhodesia's 6.7 million Africans would show up for the occasion. But most independent observers placed the crowd at less that 200,000 - smaller than the turnout given Muzerewa last year on a similar occasion.

Still, it was a colorful affair, as tens of thousands of smiling Africans sang freedom songs and waved the council flag - red with strips of black, yellow and green in the upper left-hand corner - that the bishop's aides said would become the banner of black-ruled Zimbabwe at the end of this year.

Held in the black-township of High-field on the outskirts of the capital. The welcomeing ceremony was widely regarded here as the opening of the bishop's campaign to sell the March 3 internal accord. He had left immediately after the signing ceremony for London and Washington where he tried in vain to gain backing for it.

The main tasks of the transitional government to be established are to complete a new constitution, organize national elections on the basis of adult universal suffrage, and arrange for a cease-fire in the steadily worsening guerrilla war.

The Patriotic Front, the alliance of the two main guerilla forces waging the war, has rejected the Salisbury agreement and said it intends to intensify its struggle against the Smith government and its three black "puppets."

Nationalist sources said here Saturday that British and American efforts last week to promote a new Rhodesian conference to find an internationally acceptable solution involving both the Patriotic Front and the four internal Rhodesian leaders met with little interest.

Talks were held Friday and Saturday in South Africa among British. America and Rhodesian officials to discuss such a conference, but the sources said the internal leaders were only interested in a meeting to arrange for elections under the terms of the Salisbury accord.

Muzorewa appeared undaunted yesterday by the U.N. decision not to reorganize the internal agreement. He said he had received private assurances from some members of the world body as well as of the Organization of African Unity that they would support a black majority government emerging out of it.

He decided British and American opposition to the accord and said, referring to his talks in London and Washington, "nobody has told me yet the agreement is seriously defective."

In his speech at the rally, the bishop hailed the internal settlement as marking a "genuine transfer of power from the minority to the majority" of Rhodesia and said it had fulfilled all the council's objectives. He called on all Africans as well as whites of goodwill to help build a new Zimbabwe "run by Zimbabweans of all races for Zimbabweans."

A government can now be chosen by 3.5 million voters instead of 80,000 he said, referring to the small white electorate responsible for electing the white-dominated 66-member Parliament that has ruled since this country declared unilateral independence of Britain in 1965.

Muzorewa also asked the 10,000 to 20,000 guerillas inside Rhodesia to "come home a free and heroic people" and promised them jobs, education opportunities or a place in the new national army of Zimbabwe.

Whether the guerrillas, fighting under the umbrella of the Patriotic Front, will heed his call is another key unknown in the complicated political equation. Muzorewa said reports that the guerillas were loyal only to the front were "rubbish" and that they had been fighting for a free Zimbabwe under black rule and not for any single nationalist leader.

So far, however, few guerillas have given up fighting and come home.

Muzorewa warned the front, and the front-line African states supporting the guerilla alliance, that the new interim government force with force. We shall counter every attempt to oppose the wishes of the majority," he said. "We are the power in Zimbabwe . . . we and we alone shall determine our nature."