Johnson Products Co., a Chicagobased manufacturer of cosmetics and personal grooming products that is the fourth-largest black owned company in the U.S., is investing $2.4 million in a new joint venture in Nigeria.

George Johnson, founder and president of the company, said yesterday that test marketing of Johnson products in Nigeria over the past two years indicated a potential market there that eventually could top Johnson's business in this country.

In addition, Johnson said, his company is planning to expand export and marketing activities significantly in Europe during the coming year.

"The popularity of our products in the United States has spilled over [to other nations]... we are putting emphasis on our international division, and will have two full time sales people in London, expecting considerable sales from Europe through England," he said.

Founded in 1954, Johnson Products manufactures and markets 45 hair, cosmetic and toilet products.

A significant departure in the company's business lines could develop in Nigeria, where Johnson said such additional products as deodorants and toothpastes could be produced and sold -- markets "I wouldn't try" to enter in this country, because of the multimillion-dollar investment that would be required to challenge industry giants.

The Nigerian firm, JPC-Nigeria, will be owned 40 percent by Johnson Products and 60 percent by a group of some 40 Nigerian investors from all parts of that country.

Under Nigeria's law, ownership in a business there by outsiders is limited to 40 percent. Johnson Products will operate the business under a management contract. Initially, the Nigerian firm will import products manufactured here but by the end of 1979, full manufacturing facilities will be constructed in the Lagos area and about 120 Nigerians will be employed.

Johnson sales in Nigeria currently are "several millions of dollars" a year, the company founder said.

Johnson was in Washington yesterday to receive a Commerce Department award, partly because of the international business and export activities of Johnson Products, the most extensive for any minority-owned firm.

In addition, an art collection of 13 portraits of black women, commissioned to celebrate the company's 25th anniversary, will be opened this weekend at the Frederick Douglass Museum of African Art.

Johnson, an avid art collector, began his company with a $250 loan and has seen it grow to an annual volume that reached more than $40 million before slipping sharply in fiscal 1977 to $33 million and rebounding in the past 12 months to $38.7 million.

Profits of the firm, traded on the American Stock Exchange, also turned around in the year ended Aug. 31 and totaled $2.2 million (56 cents a share) compared with $1.4 million (35 cents) the previous year.

Still, annual profits are depressed, compared with fiscal 1975, when earnings topped $5.6 million. Johnson said intensified competition among hair care manufacturers and steep costs associated with introducing a men's fragrance line contributed to the decline in 1977 while improved domestic and international hair care product sales boosted results in the past year.