Prime Minister Abel Muzorewa's government today accepted a British invitation to attend a constitutional conference next month with guerrilla forces to attempt to resolve peacefully the 15-year-old Rhodesian independence struggle.

The Patriotic Front guerrillas, who have been fighting for almost seven years in an escalating war to gain power, have not responded yet to yesterday's invitation. It is expected, however, that the guerrillas, based in neighboring Mozambique and Zambia, also will agree to attend the Sept. 10 conference in London.

The embattled, unrecognized Salisbury government attempted to put the best interpretation on its agreement to attend a conference designed to replace its constitution and, in effect, invalidate its claim to office by calling for new elections.

A statement issued after a two-hour Cabinet discussion of the invitation said the Salisbury delegation "will consist of representatives from the government." It thus ignored the diplomatic subtlety that the British invitation was issued simply to Bishop Muzorewa as an individual, not as prime minister, and that there was no reference to his Zimbabwe-Rhodesian government.

Muzorewa's government emphasized that it holds office as the result of April elections, which "were accepted by all responsible observers, including those from the (British) Conservative Party, as being free and fair." This was seen as a not-so-subtle criticism of British Conservative Prime Minister Margaret Thatcher, who has shifted away from a policy of tacit support for the Muzorewa government.

The Patriotic Front has refused to confer with Muzorewa as a head of government. The Front maintains that the bishop's black-led administration is simply a stand-in for the former white-minority government of Ian Smith, which illegally broke from Britain in 1965.

The constitutional conference is the first step in an involved process that Thatcher hopes finally will bring Zimbabwe-Rhodesia to legal independence. The plan was worked out at the Commonwealth conference of Britain and its former colonies last week in Lusaka, Zambia.

The Muzorewa government did not comment on constitutional proposals outlined by Britain yesterday that would remove the controversial power of the 250,000 white minority to block changes in the constitution and curtail the whites' ability to dominate commissions controlling the military, police, civil service and judiciary.

But government sources unofficially said today that such changes are "not an insurmountable" roadblock to an agreement.

The major difficulties, however, lie further down the road in attempting to reach agreement on a cease-fire, disposition of the rival military forces and supervision of an election -- if that stage is reached. The commonwealth left it to the British to deal with these issues later.

The sources made clear that the Muzorewa government policy in going to the conference is based partly on the hope that the Patriotic Front leaders "will hang themselves" at the talks by making unreasonable demands on the military questions.

Robert Mugabe, leader of the Front's Mozambique-based faction, said last week that any agreement would have to include the dissolution of the Muzorewa government and its military, with guerrilla forces replacing the Army.

[Mugabe, in a news conference in Luanda, Angola, reiterated this demand as the condition for accepting the British proposal -- which, however, he said he had not studied. Associated Press monitored the broadcast news conference in Johannesburg.]

Demands such as Mugabe's could only lead to a deadlock should the conference be held, the Salisbury sources said.

The government hopes Thatcher would go ahead then and call new elections anyway, which the Patriotic Front would boycott, thus presumably assuring reelection for Muzorewa, the sources said.

In the Salisbury government scenario, Britain and the United States would then lift economic sanctions and international recognition would follow, leaving the Atriotic Front to carry on the costly guerrilla war -- in which as many as 500 persons a week have been killed -- against a vastly strengthened Zimbabwe-Rhodesia.

The Patriotic Front has criticized failure of the Commonwealth plan to deal with the military issue. Tanzanian President Julius Nyerere, chairman of the fron-line African states supporting the guerrillas, made it clear at Lusaka, however, that he expected the Patriotic Front to attend the conference.

Such a conference would be the first time since the abortive Geneva Conference in 1976 that the contending sides have met to seek a solution. Past efforts to negotiate often have bogged down over whether there were any preconditions.

The Muzorewa government today reiterated its opposition to preconditions, saying it was accepting the British invitation on that basis.

The Cabinet announcement did not give any details or membership of its 12-person delegation except to say that it would consist of representatives of the government. Britain has left composition of the delegations to the two sides, but there have been reports that it would prefer that Smith, long the center of contention to the Africans, not attend.

The Rev. Ndabaningi Sithole and James Chikerema, the leaders of two internal parties critical of the Salisbury government, have demanded that their factions be represented at the conference.