Don't blame the United States Postal Service.

The final fund-raising missive from unsuccessful Northern Virginia Democratic congressional candidate Ira M. Lechner was supposed to arrive in the homes of his supporters the morning after Tuesday's elections. And it did, leaving some of his supporters confused about its timing. The letter went out because with defeat or victory still ahead, the only certainty for Lechner was debt.

"To underscore our resolve," Lechner, a Washington labor lawyer, wrote in the appeal, he and his wife, Susan, had taken a $50,000 second mortgage on their North Arlington home and lent the money to the campaign. "We did it because . . . we could not let you down by not doing all that must be done to win."

"Well, now the election is over and life goes on . . . ," continued Lechner, who by the time his letter arrived had lost to Republican Rep. Frank R. Wolf. "We remain brothers and sisters in spirit.

"I am embarrassed to ask your help once again after you have given so much, but if each of you can afford to help with another check, it will make paying off that $50,000.00 mortgage a bit easier."

Lechner campaign officials declined yesterday to comment on the letter.