The Reagan administration will ask Congress to cut off future federal legal aid for the poor, wiping out a program that now employs 5,000 lawyers across the country, has revolutionized some areas of the law and has for years been a target of conservatives, including Ronald Reagan as governor of California.

Legal aid lawyers spend most of their time handling routine civil cases: divorce work, utility cutoffs, housing, welfare, and Medicaid complaints. But in the last 15 years they have also taken on, in sweeping class actions, abortion funding restrictions, freeways, eviction rules and welfare procedures, treatment of migrant workers and of illegitimate children, and a long list of similar problems of the poor. it is these broader cases, in most of which the poverty lawyers have prevailed, that have most upset conservatives.

Edwin dale, spokesman for the Office of Management and Budget, confirmed yesterday that no further funding will be requested by Reagan for the Legal Services Corp., which disburses over $300 million a year in legal aid funds. He also said none of the money previously dedicated to legal services will be proposed for inclusion in block grants to the states.

States would be free to draw from social services block grants to fund their own legal service activities, OMB officials said. But the legal services program, as it has existed since Great Society days, would for all intents and purposes be abolished.

Legal Services Corp. officials knew their agency could be eliminated. But they had hoped that block grants to the states would include money which would have gone to the corporation, though they felt that that approach too meant, in effect, abolition.

Dale said that as of yesterday, the "decision is to make zero appropriation." He said it still would be "allowable" for states to use block grant funds for legal services under OMB proposals.

If the decision stands, a vigorous battle is expected across party lines. Senior Republicans on the House Judiciary Committee -- Reps. Tom Railsback (Ill.), M. Caldwell Butler (Va.) and Harold S. Sawyer (Mich.) -- wrote the White House last week asking that legal services be saved as ""an effective and worthwhile program for the poor." Many people regard it as the most effective of all the antipoverty programs.

Yesterday, a group of some 40 conservative Democrats, called the Conservative Democratic Forum, met with President Reagan pleading for a termination of legal services. "The program has fallen into the hands of troublemakers who forment discord in the community," said one member, Rep. Phil Gramm (D-Tex.).

Dan Bradley, president of the Legal Services Corp., said yesterday that the administration's approach to legal services "kills us any way you look at it. It will deny poor people their day in court. I just do not believe that the U.S. Congress is going to pemit legal services to go down the drain."

Legal aid supporters knew they were in trouble the day Ronald Reagan was elected. When he was overnor of California -- and when legal services were under heavy attack by Nixon vice president Spiro Agnew -- Reagan was quoted as calling legal assistance lawyers "a bunch of ambulance chasers doing their own thing at the expense of the rural poor." Following a successful legal aid suit against the state on behalf of Medicaid recipients losing beneits under Reagan budget cuts, Reagan vetoed a state grant for the California Rural Legal Assistance, citing improper representation of farmworkers, prisoners and students.

Legal assistance money was originally provided through the Office of Economic Opportunity under Lyndon Johnson's Great Society programs. It was the fist federal effort to provide systematic legal resources to poor people who could not afford to hire lawyers for non-criminal problems. The program, strongly supported by the American Bar Association as well as congressional Democrats, survived Nixon administration hostility and emerged in 1974 under what was to be the non-political umbrella of the semi-private Legal Services Corp.

Though Congress has placed numerous restrictions on legal aid lawyers and the causes they may champion, the corporation now finances 323 legal assistance projects and has been called "the largest law firm in the country."

Its grant recipients are, indeed, often amoung the larger law firms in major cities. In Chicago, for example, 90 lawyers work out of seven neighborhood offices and a central headquarters. Their salaries -- starting at $15,500 -- come from a $4.5 million budget composed 90 percent of federal funds.

The Legal Assistance Foundation of Chicago, as it is called, sees about 30,000 clients a year. A large proportion of them need help preventing utility cutoffs, or getting welfare or Social Security checks, said executive director Sheldon Roodman. But its lawyers also brought one of last year's unsuccessful Supreme Court cases chalenging the Hyde amendment restrictions on abortion funding, and foundation lawyers are currently working on reforms in numerous other areas of poverty law.

Large numbers of legal aid actions are taken against state governments, which administer many of the poor people's programs involved in disputes. This has been one of the greatest sources of outrage for conservatives.