SAN FRANCISCO, FEB. 9 -- General Motors Corp. today announced a 21 percent increase in its 1987 earnings to $3.6 billion, but only an estimated $130 million of those profits came from the company's core business, the making and selling of cars and trucks.

Those dismal earnings in its main business mean that for the second year in a row, GM will scrap profit-sharing payments to 455,200 U.S. employees eligible for those benefits.

Some 110,500 of those workers who will go without profit-sharing this year are salaried employees, while an estimated 344,700 are production employees represented by the United Auto Workers union.

Still, GM was happy to spread what it viewed as the good news -- particularly here, where many of the company's 10,000 U.S. dealers are attending the 71st annual meeting of the National Automobile Dealers Association.

The earnings announcement came at 5:30 a.m. here -- via telephone calls to reporters' hotel rooms -- three hours before the opening of today's NADA sessions.

The "good-news" alert was sounded on Wall Street a half hour before the market opened. The object there was to boost GM's stock and calm auto industry analysts who have been worrying about the company's future business plans and its shrinking share of the U.S. auto market.

But there were skeptics aplenty here and in New York.

Some GM dealers, while impressed with the company's overall profitability, were unimpressed with the sources of those profits.

GM's 1987 net income, which translated to $10.06 per share, reflects record earnings at each of its three major subsidiaries -- General Motors Acceptance Corp., the company's financial services arm; Electronic Data Systems Corp., GM's computer services operation, and GM/Hughes Electronics, a major player in GM's defense, aerospace and communications businesses.

That performance might bode well for GM's diversification strategies and for GM as a corporation, "But it doesn't bring customers into our stores," said a Massachusetts Chevrolet dealer.

GMAC announced 1987 earnings of $1.5 billion, up from $1.2 billion last year. EDS, which issues a separate "Class E" stock, had a net income of $323 million ($2.65), up from $261 million ($2.13) in the previous year. GM/Hughes, which issues a "Class H" stock, announced net income of $670 million ($1.67), up from $594 million ($1.48) in 1986.

An accounting change -- designed to better assess the value of GM's plants, tools and equipment -- contributed $800 million to GM's 1987 profits.

GM made what the company calls a "nominal profit" on vehicle production and sales. GM officials declined to define "nominal" with exact numbers. But sources familiar with the company's accounting procedures said that without the contributions from its subsidiaries and various tax breaks, 1987 net income on GM's main business amounted to $130 million.

GM's revenue for 1987 was $101.8 billion, of which $89.9 billion came from the sale of cars and trucks. The company had sales of $102.8 billion in 1986, of which $90.9 billion was generated by vehicle sales, the company said.

GM's net operating income for 1987 was $3.4 billion, up from $2 billion in 1986. Operating profits in the previous year were affected by a $1.3 billion charge to cover the costs of scheduled plant closings.

Worldwide factory sales of cars and trucks to dealers fell to 7.8 million in 1987, a 9.4 percent decline from 8.6 million factory sales in the previous year.

GM's overseas automotive operations fared better than those in the United States. Sales of GM's foreign-market products totaled $1.9 billion in 1987, compared with a loss of $600 million in 1986.

"We are particularly pleased with the dramatic improvement in our 1987 overseas results," GM Chairman Roger B. Smith and President Robert C. Stempel said in a joint statement.

Smith and Stempel said they "derive some encouragement from the fact that the North American operating groups earned a nominal profit during a transitional period of lower {vehicle production} volume and a number of nonrecurring charges, including upfront salaried employee separation costs."

Since mid-1986, GM has eliminated the jobs of 36,000 administrative and professional employees in a cost-cutting campaign. A total of 40,000 jobs will have been cut by 1990, according to the earnings report. GM currently employs 143,300 salaried people worldwide.

UAW Vice President Donald F. Ephlin, who directs the union's GM department, said the company's "continued low earnings from domestic operations obviously are a source of great concern." But he said that those lackluster numbers should also send "a signal to everyone that continued effort is needed to turn things around at General Motors."

Smith outlined a broad plan of recovery, including the introduction of a bevy of new car models this year and in 1989.

"We believe GM will turn the corner in its vehicle business, hopefully starting this year," Ephlin said.

"When that happens, our members at General Motors will receive their fair share of the profits through the enhanced profit-sharing formula" negotiated in the union's 1987 contract with GM.

.........................1983....1984 ...1985.....1986.....1987

Sales(in billions)..... $74.6...$83.9 ..$96.4...$102.8...$101.8

Net Earnings(in billions) 3.7.....4.5 ....4.0......2.9......3.6

Earnings Per Share...... 11.84...14.27 ..12.28.....8.21....10.06

SOURCE: General Motors Corp.