Sales in Northern Virginia were down 42 percent in January this year from January 1981, according to the Northern Virginia Board of Realtors. There were 623 homes sold this year, compared with 1,081 for the same month last year, the group said.

In announcing the figures, the board stated that these sales were supported by "people-to-people" financing and occurred "despite high interest rates" and "despite the cold and snow."

The average sales price rose 8 percent in the year, from $96,419 to $104,060, the group said.

Recent home sales in Northern Virginia include the following, selected at random from information furnished by Rufus S. Lusk & Son Inc.:

Fairfax

Mr. and Mrs. W. E. Slone sold a home at 10621 Maple St. for $63,000 to Mr. and Mrs. Howard Hoffman. The buyer assumed a trust of $48,550. The seller took back a note of $6,400 at 13 3/4 percent for five years.

Mr. and Mrs. C. E. Sinclair sold a home at 5419 Aylor Rd. for $105,000 to Mr. and Mrs. Jeffrey S. Renk. The buyer assumed a trust of $62,531.

M. Y. Skube and others sold a home at 3423 Brookwood Dr. for $86,900 to Mr. and Mrs. Wayne C. Cole. Guaranty Mortgage Co. placed a mortgage of $77,000 at 15 1/2 percent for 30 years.

Edward Carr & Associates sold a home at 5611 Wood Thrush Ct. for $134,950 to Mr. and Mrs. Clinton L. Williams. Weaver Bros. placed a mortgage of $128,700 at 13 1/2 percent for 30 years.

Mr. and Mrs. R. A. Parisi sold a home at 4225 Peekskill La. for $105,000 to Mr. and Mrs. David J. Wilderman. The buyer assumed a trust of $56,352. City Consumers Service placed a mortgage of $38,000 at 17 1/2 perent for five years.

Mr. and Mrs. J. C. Meister Jr. sold a home at 13236 Memory La. for $90,000 to Mr. and Mrs. Ronald C. Rush. The buyer assumed a trust of $51,000.

Mr. and Mrs. J. M. Philpott sold a home at 10201 Commonwealth Blvd. for $108,000 to Lynette C. Schonrock. The buyer assumed a trust of $67,500.

Mr. and Mrs. J. Q. Kline sold a home at 4772 Tapestry Dr. for $123,620 to Mr. and Mrs. William E. Ringer. Washington Federal Savings & Loan Association placed a mortgage of $108,600 at 13 1/2 percent for 30 years.

Foster Bros. sold a home at 10703 John Turley Place for $118,150 to Ardoke Associates. First American Bank placed a mortgage of $104,250 for two years.

Mr. and Mrs. C. Theurer III sold a home at 9525 Jomar Dr. for $115,000 to Mr. and Mrs. George H. Connor Jr. Weaver Bros. placed a mortgage of $85,000 at 13 1/2 percent for 30 years.

Vienna

Mr. and Mrs. L. G. Hummon sold a home at 233 Church St. for $133,000 to Charles M. House. The buyer assumed a trust of $40,000. The seller took back a note of $67,500 at 13 percent for three years.

Mr. and Mrs. O. S. Noel sold a home at 8423 Cottage St. for $98,000 to Mr. and Mrs. Perry G. Olcott. Kissell-Virginia Inc. placed a mortgage of $38,000 at 15 1/2 percent for 30 years.

Mr. and Mrs. S. T. McClure sold a home at 9752 Bruton Place for $135,000 to Mr. and Mrs. Gordon W. Martyn. Cameron-Brown Co. placed a mortgage of $68,000 at 15 1/2 percent for 30 years.

Z. N. Mackowitz sold a home at 236 Common Dr. for $88,700 to Gus C. Lavezzo. The buyer assumed an original trust of $35,000. The seller took back a note of $22,700 at 13 1/2 percent for three years.

D. D. Morton sold a home at 118 Dogwood St. for $91,950 to Michael I. Rieger. The seller took back a note for $80,916 at 12 percent for six years and another note for $11,034 at 12 percent for 10 years.

Alexandria

L. R. James sold a home at 3804 Elmwood Dr. for $67,500 to Mr. and Mrs. Patrick C. McFadden. The buyer assumed a trust of $38,500. Mr. and Mrs. J. M. Russo provided a mortgage of $13,700 for five years.

Mr. and Mrs. R. Buckley sold a home at 6418 16th St. for $140,000 to Dorothy P. Oxley. R. N. Adams Sr. placed a mortgage of $112,000 for one year.

Mr. and Mrs. J. Katz sold a home at 6617 Hiddenite Ct. for $97,500 to Mr. and Mrs. Edward L. McLarney. The buyer assumed a trust of $58,109. Citicorp placed a mortgage of $19,678 for 15 years.

Mr. and Mrs. J. K. Bradshaw sold a home at 5504 Helmsdale La. for $87,500 in cash to Margaret A. Sutton.

Mr. and Mrs. W. W. Davis sold a home at 1600 Revere Dr. for $91,500 to Mr. and Mrs. Leonard P. Bianchi. The buyer assumed a trust of $56,000.

Springfield

D. D. Walker, trustee, sold a residence at 8047 Sleepy View La. for $77,000 to Mr. and Mrs. Cecil I. Hamilton and others. Mellon Mortgage Inc. placed an $63,950 FHA mortgage at 15 1/2 percent for 30 years.

Mr. and Mrs. J. R. Bailey sold a residence at 7307 Walnut Knoll Dr. for $140,850 to Mr. and Mrs. Joseph C. Dawson. The buyer assumed a trust of $100,000.

Mr. and Mrs. D. A. Boor sold a home at 8166 Dark Den Center for $82,950 to Mr. and Mrs. Raymond W. Burk and others. The buyer assumed a trust for $56,642.

Burke

Mr. and Mrs. F. P. Cupido Jr. sold a home at 9773 Lakepoint Dr. for $89,000 to Mr. and Mrs. Chih-Chia Ku. The buyer assumed a trust of $81,726.

Chantilly

Mr. and Mrs. W. N. Maxon sold a home at 4005 Galesbury La. for $70,750 to Mr. and Mrs. James Beavers. The buyer assumed a trust of $25,689. The seller took back a note of $35,850 at 13 1/2 percent for five years.

Mr. and Mrs. K. P. Johansen Jr. sold a home at 4142 Hamlin Ct. for $80,000. The buyer assumed a trust of $51,527.

Mr. and Mrs. S. H. Hsiung sold a home at 13653 Stepney La. for $80,000 to Mr. and Mrs. Lloyd C. Atkinson. The seller took back a note for $65,000 at 11 to 13 percent for five years.