Ian Smith, who for years fought the world in refusing to grant black-majority rule in Rhodesia, is apparently staging his last stand, ironically in growing isolation from the white community for whom he was so long a hero.

True to form, however, the former prime minister is not going down without a fight at the 10-day-old British-sponsored Rhodesia settlement conference.

Key whites in the Zimbawawe-Rhodesian delegation said today that the "crunch" must come by the end of the week when Prime Minister Abel Muzorewa plans to leave the talks temporarily: Either Smith gives in on his insistance for a white blocking power on constitutional amendments or the Salisbury administration is in real trouble.

Late in the day Smith showed signs of backing away from his hard-line stance saying in a television interview he requested, "I don't want people to think we are going to dig in our heels, irrespective." It was vintage Smith tactics -- playing tough and then testing the waters for compromise often after tarnishing the atmosphere for negotiations.

Earlier in the day, he was a lone "eloquent" figure as he doggedly tried to convince British Foreign Secretary Lord Carrington that the 230,000 white minority in the war-torn country must retain the power to block constitutional changes under a black government.

British sources made it clear that his argument fell on deaf ears, not only to Carrington but also to other members of the mixed-race Zimbabwe-Rhodesian delegation.

Probably most disturbing to Smith, the darling of the embattled whites since his illegal declaration of independence in 1965, is the mounting evidence that his own people feel he has outlived his usefulness.

Whites both inside and outside the delegation are increasingly open in their criticism. Significantly, however, none will speak for attribution.

One delegation member who has worked closely with Smith for years described him as a "frustrated, embittered" man who "has done his job and now should bow out." He added that there was lots of criticism by whites in Salisbury about Smith's inclusion in the delegation on the basis that he could be a disruptive force in the talks.

One place where Smith is still a bona fide hero is among the right-wing British community. Last night hundreds of Britons, all white, paid $28 apiece to cram into a hotel ballroom for a reception for the Muzorewa government sponsored by the Anglo-Rhodesian Society.

There was no question who the star attraction was. Smith, besieged by admirers and under the glare of television cameras, sat at a table for more than an hour signing autographs for his worshipping audience. Muzorewa shook a few hands and left after less than half an hour.

A sympathetic cocktail waitress remarked, "It must be difficult for Muzorewa to see Smith getting all the attention."

Smith's critical colleague said the admiration "had gone to Smith's head."

After being banned for 14 years in Britain as a traitor he now "gets fan mail, enjoys the pomp and loves to hear the cries of 'Good old Smitty, keep it up.'"

"He's mingling with over-the-hill politicians in Britain who are telling him to stick it out. They're not doing us any good."

The delegate put the dilemma for the Zimbabwe-Rhodesian government bluntly: "Either we go back with a settlement or without one . . . I'm not going back without one."

If there is no settlement, he said white flight, which is already averaging 1,000 a month, will escalate sharply. "The young are sick and tired of the war: they want a decision," he said.

The delegate admitted the current British negotiating position is, "the worst offer we've ever had." He added, however, that the alternative was to get even a worse deal later.

"We're on a hooker," he said. "We either carry on alone and die or we take something that offers the opportunity to survive and live."

Disagreeing with Smith on the constitutional issue, he said, "I don't believe that the blocking mechanism is all that valuable. We have a built-in blocking mechanism because of the division in the black community" no matter how many white seats there are.

It was disclosed in today's talks that Britain is suggesting a black-white ration of 80 to 20 in parliament with 70 percent approval necessary for amending the constitution.

The source said it was obvious from the conference that in order to lift sanctions and get recognition "we won't get away without new elections." he voiced concern that Smith's tactics, in putting Muzorewa on the defensive about white rights, would hamper the bishop's election chances.

"Murorewa is a product of our creation. We must back him," he added.

A basic problem for Smith is that at heart he does not think that blacks can or should rule and he has "never given up that belief," the delegate said.

The whites would face a problem if the Patriotic Front guerillas enter into an agreement with the British and the Zimbabwe-Rhodesian government, but the delegate felt that this was unlikely. He acknowledged that so far the Front was "getting the upper hand" in the talks.