Guerrilla leader Robert Mugabe warned today that British tactics in the Rhodesian settlement conference could lead to his Patriotic Front Alliance's accepting a proposed constitution only to "tear it up" after gaining power.

The Front wants to deal with the British-proposed constitution it opposes "in an honest manner," Mugabe said in an interview, but found it difficult because of Britain's insistence on certain safeguards for the 230,000 white-minority population.

He objected to British Foreign Secretary Lord Carrington's efforts to force both the guerrillas and the Zimbabwe-Rhodesian government, who are locked in a bloody war, to accept the draft constitution by Monday or risk a breakdown of the four-week-old conference.

Acknowledging that Carrington is trying to pressure the Front into acceptance, Mugabe said, "We are not going to be threatened into a yes-or-no deal. We've come here to negotiate and negotiate we shall."

"We are not threatening anyone," he added. "We want the conference to continue."

Mugabe's threat to ignore an agreed constitution could have serious repercussions on Carrington's efforts to achieve a spirit of reconciliation in this ninth attempt to settle the intractable independence problem, which began when the white government of former prime minister Ian Smith illegally declared independence from Britain in 1965.

"The manner in which Lord Carrington is going about [the conference] creates room for us to just dishonor the constitution and tear it up," Mugabe said.

"We'll let him know in advance we don't agree to certain provisions of the constitution and we won't honor them. No one tomorrow should accuse us of dishonoring the constitution because we will have said so in advance."

He added, however, "In all honesty, why should we have to use untoward methods. We want to go about it in an honest manner."

Complaining about constitutional prohibitions on changing white ownership of land, which he called "the most crucial aspect of our economy," Mugabe said the future government "must now have it hands fettered."

Aside from his sharp criticism of the British draft constitution, Mugabe, 54, who was detained for 10 years by the previous white Rhodesian government, generally was conciliatory in the wide-ranging interview.

Speaking at the apartment where the leadership of his Zimbabwe African National Union has its conference headquarters, Mugabe:

Said a Patriotic Front government would make major changes in land ownership, control of the economy and education, but he added that any new government "must take into account the realities that exist in the country and accept the status quo for a while."

Acknowledged that no new government could "start by abruptly cutting off the established system of trade" between Zimbabwe-Rhodesia and South Africa. Pretoria gives vital military support to the Zimbabwe-Rhodesian government of Prime Minister Abel Muzorewa in its war against the Front. Mugabe said, however, "as neighbors there must be a realization that we must coexist.

Strongly defended his Marxist-Leninist policies, saying they provided the best system for an independent Zimbabwe. A practicing Catholic, Mugabe specifically differed with Marxist doctrine on religion, praised humanitarian aid by churches for the guerrillas and said a Front government would "allow free play to churches."

Said he tentatively planned to visit the United States later this month to attend a conference on Africa at Hot Springs, Va. He pointedly added that he would welcome high-level talks with officials in Washington.

The general tenor of the remarks fit with a new image Mugabe has cultivated during the last year as more moderate and less anti-Western, despite the military aid he receives from communist nations. There has been no significant sign of any change, however, in the principles espoused by the quiet Zimbabwean, who shares leadership of the Patriotic Front with the garrulous Joshua Nkomo.

Mugabe directed its strongest criticism at British proposals entrenching white representation and protecting white control of the best land for seven and 10 years, respectively, unless Parliament unanimously approves amendments.

"Even the angels in heaven don't always vote yes," he said.

He charged that British attempts at reconciliation are one-sided and at the expense of Zimbabwe-Rhodesia's 6.8 million Africans.

Britain is saying, "Do nothing to the whites, leave them in a privileged position," he said. "How much of the wishes of our people and the sufferings which they have undergone over the years are you taking into account?"

He said he did not regard Monday's meeting as a final chance to reach agreement on the constitution, pointing out that a breakdown in the talks would cause Carrington problems at next week's Conservative Party conference where he faces right-wing criticism already.

The front, he added, was still working on its reply to Carrington, and he declined to give details.

Mugabe acknowledged the possibility that Britain may bypass the guerrillas and go ahead with the Muzorewa government to implement the constitution if the Front continues to hold out.

"They can go ahead and we'll go ahead with our war," he said.