Weaver Bros. Inc. recently arranged more than $5 million in wraparound mortgage financing with General Electric Credit Corp. for the owners of the 40-story Saint Paul Building at 222 St. Paul Place in Baltimore. The Saint Paul contains 68,250 square feet of office space and 231 apartment units. The major tenant is the Baltimore and Ohio Railroad. William C. Smith Co. is the owner-manager of the development.

* Italian Aerospace Industries Inc., a subsidiary of Aeritalia, has leased space at One Crystal Gateway in Crystal City. The lease was negotiated by John H. Brody, assistant vice president of the Charles E. Smith Cos.

* Yorktowne Business Institute has signed a lease with Coakley & Williams Inc. to occupy 8,000 square feet of office space in the new Maryland Trade Center Building located at the interchange of the Baltimore-Washington Parkway and the Beltway. Yorktowne is a postsecondary proprietary business school that teaches word processing and data processing.

* Executive Boulevard Association Inc. has purchased 12.99 acres of land on Executive Boulevard in Montgomery County for $5 million from Science Investors Joint Venture. Gillian Keenan, a broker at Coldwell Banker Commercial Real Estate Services, represented the buyer and the seller.

* The Braedon Cos. announced that Union Carbide Corp. has leased more than 9,000 square feet of commercial office space at 1100 15th St. NW. The company has taken the top floor of the building at the corner of 15th and L streets NW on a 10-year lease with an aggregate value of more than $2 million. The building, owned by Prudential Insurance Co. of America, is about 60 percent leased and scheduled for occupancy in February 1982.

* Julien J. Studley Inc. has completed the following leasing arrangements for an aggregate value of $1.5 million: NPS Energy Management Inc. leased 3,200 square feet at 1090 Vermont Ave. NW; National Medical Association leased about 2,800 square feet at 1301 Pennsylvania Ave. NW; Nestle Inc. leased 2,700 square feet at 1900 M St. NW; and Lou Harris Agency leased about 1,000 square feet at 1090 Vermont Ave. NW.