THE FEDERAL NATIONAL Mortgage Association and the Federal Home Loan Mortgage Corp. have raised the maximum size of the mortgage loans they will purchase this year.

On Tuesday, the new loan limits became $115,300 for mortgages on single-family homes (up from $114,000); $147,500 for two-family houses (up from $145,800); $178,200 for three-family houses (up from $176,100), and $221,500 for loans on four-family properties (up from $218,900).

Maximum loan amounts for mortgages on homes in Alaska and Hawaii are 50 percent higher.

And in the case of Fannie Mae, which can buy second mortgages, the limit on those loans rose from $57,000 to $57,650 ($86,450 in Hawaii).

Where Fannie Mae owns both the first and second, the total of the two notes may not exceed the limit on firsts.

The loan limits are set by law and adjusted each year to offset the effects of inflation. Kenneth Thygerson, president of Freddie Mac, said "the modest increase in this year's limit reflects the fact that house prices were relatively stable over the past year."

MAGIC JOHNSON has moved into his new, two-story, 8,000-square-foot home on half an acre in the Bel-Air section of Los Angeles. And thanks to its high ceilings, the 6-foot, 8-inch Laker guard needn't stoop when inside.

He needn't go far to shoot a few baskets, either. The country English-style house has an indoor sports area with a racquetball court that he converted to a basketball half-court.

Johnson is apparently family oriented. Before he bought the house, his parents came out from Michigan to approve it.

Then he bought the property for nearly $2.35 million (the asking price).

IN THE BUSINESS . . . Signature Communities has opened a furnished model for its Huntley Estates project in Alexandria, which features detached houses priced from around $120,000 . . . The first of two twin towers that will be the American Center in Tysons Corner has been topped off. The 318,000-square-foot office complex, a joint venture of the Property Co. of America and Metropolitan Life Insurance Co., is scheduled for occupancy next April.

PERSONNEL FILE . . . Weaver Bros. Inc. has named Martin R. West III senior vice president of its mortgage banking division, and has named Cornelius (Neal) Armstrong sales coordinator for the commercial sales and leasing department . . . Stephen B. Patterson has been named vice president for sales and marketing in the mortgage-backed-securities division of the Federal National Mortgage Association.

ON THE MOVE . . . The Flower Avenue Shopping Center in Silver Spring has been sold by Lopez Enterprises Inc. to Joseph K. Melrod for $2.6 million. Cassidy, Jaeger & Pinkard Inc. was the broker in the transaction . . . The Heritage Foundation has completed subleasing the space that it is not occupying in its newly renovated headquarters at 214 Massachusetts Ave. NE. Among the tenants: Adolph Coors Co., Amway International, and the Saturday Review. Jason Corp. has been the leasing broker for the project.