Chile's main labor, white collar and community organizations have challenged President Augusto Pinochet to solve the country's economic and political problems or face the most serious campaign of civil disobedience since he took power in 1973.

The ultimatum came at the newly formed National Civil Assembly, whose 278 delegates gathered in secrecy yesterday at a Jesuit retreat outside Santiago, after the city's military commander, Army Gen. Carlos Ojeda, banned the meeting from a downtown theater.

The assembly followed weeks of sporadic and sometimes violent antigovernment protest, following opposition pledges to make 1986 the "decisive year" for the regime. In the past two weeks, about 1,000 persons have been arrested, mostly students protesting military intervention in the universities. Troops in combat gear and with blackened faces have been deployed against such protests.

Assembly participants said a principal purpose of the meeting was to take the lead that Chile's opposition parties, bogged down in tactical and ideological disputes, have proved incapable of providing despite recent church-sponsored attempts to bring them together.

Observers here said that this lack of a clear political alternative is the opposition's critical weakness, despite growing civilian discontent with Pinochet. Assembly delegates hope the threat of civil disobedience may encourage opposition groups to press their political demands on the government.

Delegates to the assembly -- from center right to communist left -- represented all major labor unions, professional and student organizations, peasant farmers, native Indian communities and human rights organizations. It was the broadest such gathering since the military took power, according to observers.

Militant students, fresh from recent street battles with riot police, sat alongside conservative shop and truck owners who had taken the lead in supporting Pinochet's 1973 coup.

Larger business and farming interests did not take part. Pinochet retains support among those groups, whose members are closer to the government and less dissatisfied with its policies and who do not subscribe to civil disobedience.

At its day-long meeting, the assembly approved a 50-point petition, called the "Demand of Chile," which makes up a virtual alternative program of government. The document calls for the lifting of emergency measures, the abolition of the secret police, a democratically approved constitution, slashed military spending, the end of military control of the universities, freedom of expression and compensation for victims of human rights abuse.

The petition also proposes public works to absorb record unemployment, industry-wide collective bargaining, and the renegotiation of the country's $20 billion foreign debt "to eliminate the net transfer of resources abroad" and "assign foreign earnings to the solution of national problems."

In a warning to the military, the petition added: "If the present situation continues, it is easy to foresee growing confrontation in which the armed forces will be seen to be irreversibly involved in repression of such magnitude that it will dissociate them definitively from the people and endanger their institutions themselves."

"We favor peace, not war -- but we know that neither our country nor peace can be won without struggle," said the assembly's president, Dr. Juan Luis Gonzalez, president of the National Medical Association. He set a deadline of May 31 for the government to respond to the "demand," after which the delegates promised to unleash mass civil disobedience.

Protest methods being planned include withholding debt repayments to banks, street demonstrations and, possibly, a general strike by the unions.

[The unions have vowed to mark May Day on Thursday with an illegal rally, The Associated Press reported. Leaders of 28,000 truck owners have decided to halt payments on $200 million in debts next month, while 150,000 homeowners were to vote today on whether to suspend payments on government-financed mortgages.]