Citigroup, the fifth-biggest U.S. mortgage originator last year, is cutting about 1,000 jobs in its home-lending business, including about 100 in Irving.Most workers affected by the layoffs will be reassigned to other work at the site, said Mark Rodgers, a Citigroup spokesman. While difficult, these actions reflect our ongoing efforts to increase operational efficiency, adapt to changes in the marketplace and position the business for the future.The Irving jobs being cut are in mortgage fulfillment, while other workers handle sales, underwriting and defaults, the New York-based company said Monday in an e-mailed statement. Las Vegas will be hit hardest with 750 positions lost, and another 150 positions will be affected across the country, mostly work-from-home jobs. Rodgers said Irving employees who are not reassigned will work until Nov. 22, after which they will be paid for two months. They then will receive severance based on years of service and be offered job transition benefits, he said.After the layoff, Citigroup will have about 5,700 workers at its Irving facility, including some in mortgage operations but primarily in credit card and other functions, Rodgers said.Citigroup is the Regent Commons office complex at Interstate 635 and Belt Line Road. In 2006, Citigroup built 620,000 square feet of office space in three buildings on the 52-acre site. It received a 15-year, 60 percent tax abatement from the city of Irving.Citigroup sold the campus in 2012. Most of the space is leased to State Farm Insurance, according to reports.Citigroup joins Wells Fargo and Bank of America in trimming home-lending staff after refinancing fell more than 70 percent since September 2012. It announced the closing of a Danville, Ill., facility in July, leading to 120 job cuts, and fired some telephone sales agents, the company said earlier this month.Separately, it is hiring employees to originate new mortgages for home purchases as opposed to refinancing, a source told Bloomberg News.Bank of America is eliminating 2,100 jobs and closing 16 offices by Oct. 31, two people with direct knowledge of the plan said this month. Wells Fargo said in August that it will cut 2,300 jobs in mortgage production. The share of applicants seeking to refinance declined to 57 percent in the week ending Sept. 6, the lowest since April 2010, before rebounding to 60.9 percent the next week, according to the Mortgage Bankers Association. Citigroup made $65 billion in mortgages last year, or about 3.4 percent of the total market, according to Inside Mortgage Finance, a trade publication. Staff writer Sandra Baker contributed to this report, which includes material from Bloomberg News.