The all-white Republican Front party of Ian Smith, who led Rhodesia--now Zimbabwe--into a futile war to prevent black rule, split today in a move that may finally end the former prime minister's tight grip on political power among the country's 180,000 whites.

Seven of the party's 20 members of Parliament resigned from the front, saying, "We no longer believe that we are able to represent our constituents adequately as members of the party."

The seven said in a statement that they would remain in Parliament as independents. A spokesman said that working as individuals they hoped to "win the confidence" of Prime Minister Robert Mugabe, who led the war against white rule and became the first black prime minister of independent Zimbabwe two years ago.

Smith, reduced in the last three years from prime minister to the leader of a demoralized white community, said it was "a sad day." His face puffy and haggard, he added, "There couldn't be a worse time for this to happen."

The remaining members, he said, "will continue and perhaps be more dedicated to the role they have to play."

Smith has frequently talked of stepping down from the party leadership, but today he said that "the time to resign has passed," and added that this move may keep him in politics longer than he expected because, "when there is turmoil and people are upset, more than ever you have to stand by your post."

But many whites simply have turned off to politics since the advent of black rule. Others are seeking an alternative to Smith, 62, since Mugabe has made it clear he is willing to include additional whites in his Cabinet but not members of Smith's party.

A source close to Mugabe said tonight that one or two of the Republican Front dissidents would probably get Cabinet posts. He thought that Chris Anderson, former justice minister under Smith, was the most likely candidate.

The other six who resigned from the Republican Front are former agriculture minister William Irvine, James Thrush, Paddy Shelds, Rodney Cartwright, Henry Ellsworth and Esmond Mickelm.

Thrush, who acted as spokesman, read a statement by the seven after a caucus of the party.

"Our decision," the statement said, "has been reached after many months of discussion . . . in particular, as to whether or not the RF has been able to adapt itself to the changed circumstances."

They gave as another reason for the rift, "views wholly opposed to ours held by certain members of the caucus." This was taken to mean remarks, sometimes verging on racism, made by some front members during exchanges with Mugabe's representatives in Parliament.

Thrush said it was "odious" to be associated with the political philosophy of some front members, but he declined to elaborate.

Neither he nor Anderson, who was interviewed separately, cited any specific policy differences with the front.

The differences "are not so much a question of policy but rather approach," Anderson said. "The connotation of the Republican Front is with the past rather than identifying with the present and the future."

Smith frequently has criticized the government and repeatedly has declined to say anything favorable about the Mugabe administration, despite significant advances in social welfare. In addition, he regards the era of white-run Rhodesia as "one of the proudest histories ever recorded"--an attitude that is at sharp variance with the government, which cites numerous examples of discrimination against blacks then.

The Rhodesian Front was formed in 1962 and gained power the same year under prime minister Winston Field. Smith led a right-wing revolt in 1964, ousted Field and became prime minister.

A year later he unilaterally declared independence from Britain, bringing international opprobrium and economic sanctions upon his country. Nevertheless, Smith was an object of hero worship by most whites.

Eventually blacks took up arms in 1972 in a seven-year guerrilla war that led to a negotiated settlement and an elected black-majority government under Mugabe.

Whites are guaranteed 20 of the 100 seats in Parliament, and they were all held by Smith's party until today. In fact, Smith's party has never lost a seat at the polls since he was elected 18 years ago.

He survived several previous party rifts and emerged stronger. But in those cases he had the advantage of being in power and he was challenged by hard-liners rather than by those wishing to make accommodations with a black government.

Still the dissidents tred cautiously today.

"I have a tremendous feeling of warmth, affection and respect toward Mr. Smith," Thrush said.