Securitization of adjustable-rate mortgages in the first quarter cooled down slightly from the record pace set over the second half of 2004, but ARMs remain a major force in the MBS market, according to a new analysis and ranking by Inside MBS & ABS. A total of $205.3 billion of ARMs were securitized during the first quarter of 2005, down 5.0 percent from the final three months of last year. But that was still the…