Since the beginning of American settlement here, the Irvines have been a dominant force in Orange County. But last week, with the sale of the Irvine holdings to a consortium of businessmem from across the nation that era has come to an end.

The Irvine Co. bought for $337.4 million by 10 business investors headed by Detroit shopping center developer Al Taubman, owns 80,000 acres or one-fifth of Orange County, one of the largest tracts of privately held underveloped suburban land in the nation. Three investors, Joan Irvine Smith and Mr. and Mrs. Keith Gaede, are the only partners with any family relationship to the original Irvine founder.

The sale of the Irvine properties, controlled by the family since 1876, has caused tremors up and down this county of 1.7 million. "I guess it's like getting a new landlord in an apartment building." explained Irvine Co! president Ray Watson. "Suddenly we've got a new owner in the county and evrone's concerned and floating in a netherworld."

The consotium, which is expected to take operating control of the company after June 25, captured the Irvine properties after a year-long bidding war with several firms carried out at the insistence of Joan Irvine Smith, currently the largest company stockholdler with 22 per cent of the stock. Finally, the last of the other bidders, Mobil Oil Corp., bowed out, claiming that the bids had gone so high as to make the Irvine purchase "economically infeasible."

The Taubman group now takes over Irvine Co.'s plans to build the largest privately designed development in the nation. By the end of the century, the Irvine plans call for some 40 residential villages here with a total population of up to 450,000, two shopping centers and a host of medical, educational and industrial facilities.

Today some 57,500 people live in a few isolated developed clusters on the ranch which abutts the southern edge of this sprawling Los Angeles basin. Homes in the area sell for from $60,000 to $250,000 and are in such demand when 285 Irvine Co. homes opened last June, 6,000 families signed up to buy them.

Such masses of people would have seemed inconceivable when James Irvine first came to this land of rolling hills, looming mountin peaks and rich fetile coastl plains during the Civil War.

Originally and impoverished Irish immigrant, Irvine came to California in search of gold but instead made a more modest fortune as a wholesale merchand in San Francisco. Searching for rangland for sheep, Irvine and the three other men started buying out the original Spanish ranchos here.

These originla settlers, some deving their ownership from the king of Spain, sold out one by one as they fel increasingly into debt to Anglo-American merchants in nearby Los Angeles. By 1876 James Irvine also had bought out his partners.

For nearly the next centuary the Irvines developed a vast ranching and farming empire, including a 100,000-acre ranch in Montan.

James Irvine Jr., the only son of the founding father, incorporated the rach in 1884 and, on the advice of his accountant, gave control of the company to a foundation established in his name.

In 1947, James Irvine Jr. was found dead, floating face down in a stream on the company's Montana ranch. According to his grand-daughter, Joan Irvine Smith, the death took place right after a violent argument between the elderly Irvine and W.B. Hellas, then company vice president.

Twelve years later another family heir, Myford Irvine, was discovered dead in the basement of his home on the ranch, two shotgun blasts in his stomach and a .22 calibre pistol slug in his head. Officially declared a suicide, Joan Irvine Smith claims the death came with some "financial difficulties which caused him to considerable worry."

Despite these family tragedies, the Irvines attained their preeminent position in Orange County until recent years. Close linked to the powerful Orange County Republican establishment, the Irvines, political veterans here concede, maintained a firm hand over local politicians.

"They've been so equated with this county that we used to call it Irvine County and that about tells it all," said Francis Robinson, a Newport Beach environmentalist and longtime foe of Irvine development plans. "In the old days if you didn't do what the Irvines said, you didn't do anything."