Boston real estate owners should strongly support the efforts of the directors of the National Association of Realtors, who met last week in Orlando, FL to sign a stimulus proposal that includes a temporary $7,500 tax credit for all buyers. Unlike the current government plan, which is limited to first-time homebuyers, this would be a true tax credit and not a loan. The $7,500 would not need to be repaid. The plan proposed by the National Association of Realtors also calls upon the federal government to make permanent the temporary increase in FHA, Fannie Mae and Freddie Mac loan limits to $729,750 in high-cost areas. These limits are scheduled to roll back to $625,000 on Jan. 1.