Melissa Gilbert Tells Judge Timothy Busfield Has 'Strongest Moral Compass'

Timothy Busfield -- accused of child sex abuse -- has a strong moral compass, and he's universally loved by professional colleagues ... so says his wife, Melissa Gilbert.

The "Little House on the Prairie" star vehemently defended her husband in a letter to the judge in his case while the court weighed whether to allow him out of custody prior to his trial.

In the letter MG describes Busfield as her "love" and "rock" in both business and life ... adding he's the "beating heart of our wild and wonderful extended family."

She then writes that she knows Busfield more intimately than anyone else in his life ... and he "has the strongest moral compass of any human I have ever known." She adds ... "He has dedicated his spiritual self to always being of service to others. He starts every day with kindness and compassion."

To prove his kindness and compassion, Gilbert claims she's heard from multiple people he's worked with that he's their favorite director ... and tons of former students have also sung his praises to her while out in public.

She also details Busfield's relationship with her son, Michael Boxleitner, who he's "nurtured and guided" since her boy was just a teenager.

Speaking of Michael, he also wrote a letter in support of Timothy ... referring to him as a "hero" -- showing up for him more often over the last 15 years than his biological father, actor Bruce Boxleitner, ever has.

Boxleitner lauds Busfield's "stalwart integrity," and says there is "no man on this earth more worthy of respect, kindness and care in [Michael's] eyes."

As you know ... Busfield surrendered to authorities in New Mexico earlier this week after a warrant was out for his arrest -- which alleged he sexually assaulted two kids on the set of "The Cleaning Lady."