Faced with a contempt-of-court threat, Westchester County’s top executive says the county will seek to reintroduce legislation forbidding landlords from rejecting tenants who receive federal rent subsidies. County Executive Robert Astorino told a court-appointed monitor Thursday of his plans. The legislation is a key provision of a 3-year-old fair housing settlement. Federal Judge Denise Cote earlier this month ordered the county to disclose its plans to comply with an earlier court order to push “source of income” legislation. After the county said it would await the outcome of an appeal, the top federal prosecutor in Manhattan threatened the county with contempt of court. Cote had ruled Astorino violated the 2009 agreement when he vetoed a source-of-income bill in 2010. The original settlement required that the county executive “promote” the legislation.