NEW YORK (AP) _ The president and chief executive of Matilda Publications Inc., which publishes Ms. and Sassy magazines, has resigned from the privately-held concern she helped found a year ago, the company announced.

Sources close to the company said Tuesday that the publishing concern was looking for someone who may be willing to invest in Matilda Publications.

Sandra Yates resigned Friday and left the staff a memo in which she said she was leaving to ''begin work on other publishing projects.''

''I leave confident of the future prospects of Sassy and Ms. magazines, both of which are doing well and continue to flourish,'' she wrote.

A call was placed to Ms. Yates, but she was said to be unavailable to elaborate on her reasons for leaving.

The board of Matilda Publications appointed Carla Graubard, Matilda's chief operating officer, as acting chief executive until a successor to Ms. Yates is found. Ms. Graubard did not return a telephone call.

The board also said Anne Summers, editor-in-chief of Ms., will assume editorial responsibility for both Sassy and Ms.

Ms. Summers, who was Ms. Yates' partner in getting Matilda started last June, said she would not speculate about her partner's reasons for leaving.

Ms. Summers said the company was ''in the process of doing a refinancing'' and has for been looking for ''a couple of months'' at the possibility of bringing in ''a new partner who has some publishing experience.'' She declined to say what conditions led to the search, but said it would be incorrect to say that the company had been placed on the auction block.

Matilda's current financial backers include Citicorp's Venture Capital Fund and Australia's State Bank of New South Wales.

Ms. Yates had introduced Sassy, aimed at teenage girls, to the United States in March 1988 as a publication of John Fairfax Ltd., which is based in Australia.

Sassy had a circulation of about 437,000 at the end of 1988, while Ms. has a circulation of about 550,000, Ms. Summers said.

Matilda Publications was formed in June 1988 and bought Sassy and Ms. from Fairfax for a reported price of about $15 million.