The latter-day descendants of two early immigrants to Texas have taken the first step in converting a big tract of ranch land, studded with 150-year-old oaks and grown over with prairie grass, into a modern multi-million- dollar subdivision.

Mangum Manor, a $6,500,000 addition bordered by Mangum Road and Brickhouse Gully, will spring up on land that hasn't changed hands in the last 150 years. The tract is northwest of the city and just west of Oak Forest.

Gasper DeGeorge, representing the DeGeorge Estate in the DeGeorge and Associates firm of developers, has bought the historic tract from the heirs of the Sauer family, who have owned it and lived on it through several generations.

Reinhold Sauer, 83, and Guy Moss, two of the scions of early Dutch settlers, who first obtained the land under Spanish Land Grant when Texas was a Republic, represented the sellers. The sale of the 109-acre tract was consummated for a reported $300,000.

Still standing on the land, but impending sacrifice to progress, is the old handmade manor house build by R.C. Sauer in the early 1800's. "Wood in the house was hewn from the actual site," said Mr. DeGeorge. "The settler actually built the house himself from the natural resources here."

A modern $7,000,000 subdivision will replace this early American home built by a Dutch settler Reinhold Sauer, in the early 19th century. Casper DeGeorge has bought the 109 acres surrounding the homestead and will begin Mangum Manor in January, 1955. Its the first time the land has changed hands since Texas Republic days and the first time a Sauer heir hasn't lived on it.

The old mansion is colonial in the truest sense of the word, with tall columns supporting the overhang on the wide veranda. Its steep roof is made of hand-split cedar shingles said to have been cut from wood selected in the surrounding woods. The house sits in a clump of ancient cedars, live oaks and pines facing a clearing for farming and grazing still marked with the smoldering remains of the primitively charred stumps from clearing.

Brickhouse Gully, a deep gulch on the north side of the property, got its name from a brick house used for changing stagecoach horses.

The dilapidated manor house and its collapsed outbuildings, deserted for more than a decade, will be torn down before the first of the year, when paved streets with curbs and storm sewers will begin to replace the wagon-wheel lanes that have moved overland for more than a century.

Mr. DeGeorge, whose grandfather also was an immigrant, but from Italy, represents the second generation of an important Houston development family. The family has been known for building, commercial development and hostelry. His associates include Allen J. Sacco, Frank Reinhart, Jack R. Little and James B. DeGeorge, a brother.

"We will spend some $350,000 on development of streets, curbs, gutters, lights, storm sewers, etc. and will build around 20% of the 400 homes planned," Mr. DeGeorge said.

Homes will be in the $12,000 to $15,000 price range on FHA and VA-insured loans and will be built on homesites of a minimum size of 60 by 110 feet.

All utilities will be furnished by the city and according to city specifications, since the addition will lie within the northern city limits.

Space had been reserved for a $400,000 shopping center and a six-acre tract has been set aside for a possible future city park.