UPDATE 1-GM appeals direct to employees as strike losses pile up

(Adds GM's plan to boost investment in U.S. plants)

Oct 11 (Reuters) - General Motors Co took the unusual step of appealing directly to employees in a blog post on Friday that laid out the terms of its latest offer aimed at ending a month-long strike.

While emphasizing GM's commitment to the collective bargaining process, the letter, signed by Executive Vice-President for Global Manufacturing Gerald Johnson, circumvents United Auto Workers (UAW) leadership and points to frustration at a lack of progress on ending a conflict that has already cost the company more than $1 billion.

GM also boosted the amount it plans to invest in its U.S. plants to $8.3 billion, up from its previous offer of $7 billion, a source familiar with the company's offer said.

Of the new total, $7 billion would be invested directly in GM plants, with the rest going to joint ventures including a potential battery plant near the Lordstown, Ohio, factory that has been idled.

"The strike has been hard on you, your families, our communities, the company, our suppliers and dealers," GM's letter read, saying the latest offer increased compensation and promised a path to full-time jobs for temporary workers.

"We have advised the Union that it's critical that we get back to producing quality vehicles for our customers. (...) Our offer builds on the winning formula we have all benefited from over the past several years."

A UAW spokesman declined to comment on the new GM offer. (Reporting by Ankit Ajmera in Bengaluru and Ben Klayman in Detroit; editing by Patrick Graham and Saumyadeb Chakrabarty)