A giant publishing house and a powerful New York legal newspaper are planning to move into a growing and untapped market this spring by starting competing weekly tabloids covering news of the nation's 450,000 lawyers.

There presently are no newspapers covering law - the country's fastest growing profession and one that is in the midst of great internal turmoil and change - on a nationa basis.

Local law journals, including the 106-year-old Washington Law Reporter, are more concerned with printing court calendars and profitable legal advertisements than in covering the more controversial new trends in professional practice.

These two new weeklies aim to fill that void. At the same time, they are a further indication of the growing impact of U.S. laws and regulations on the practice of law throughout the country - from the big city firms that once shunned a Washington practice, but now are being forced to open offices here, to small town, attorneys who find their clients need expertise in the latest federal environmental, work safety or equal employment opportunity rules.

"Government regulations used to only affect the General Motors of the country, but now they affect medium-sized firms in Kalamazoo," observed Lewis A. Engman, former chairman of the Federal Trade Commission who now runs the three-attorney Washington office of a Grand Rapids, Mich., law firm.

Moreover, there is a growing feeling among lawyers across the country that the day of an attorney setting up practice on his own is fast ending. Instead, many lawyers feel, firms will become larger and larger. Some predict a day when there will be the big national law firms with offices in cities all over the country similar to the major accounting firms or the H & B Block firms for income tax.

"In 15 years," one lawyer said at last month's American Bar Association meeting, "the practice of law will be unrecognizable."

Nowhere are these changes occurring faster than in Washington, where leading firms such as Covington & Burling are growing so large (200 attorneys now, up 35 in three years) that associates and partners often have to be introduced to each other at local Bar Association functions.

"Washington is still a place where five people can develop expertise in a specialty on the Hill or in the agencies set up a firm and grow like crazy," said one New York observer of the Washington legal scene.

It is these new trends that spurred the creation of two new legal weeklies aiming at different, but overlapping, markets.

The publishing firm, Harcourt Brace Jovanovich, currently is hiring editors for a weekly tabloid catering to Washington's booming legal community - which now consists of about 25,000 government and private attorneys and is growing each year - as well as lawyers across the country trying to keep abreast of legal affairs in Washington. The paper will be headquartered in Washington.

At the same time, the daily New York Law Journal is planning a national newspaper - the only one in the country will cover trends in law practice all over the country.

The paper will be headquartered in New York, and although it will have news bureaus in Houston, Chicago and Los Angeles - all national legal centers - a bulk of its reporting will come from its Washington staff.

As their chief editor, they have hired David Beckwith, who covered legal affairs for Time Magazine.

Plans for the two newspapers sound remarkably alike, as well they might since Stephen A. Glasser, who with his wife Lynn, will publish the Washington law weekly, worked until recently as executive editor of the New York Law Journal.

The New York Law Journal's weekly will be edited by Josh Fitzhugh, a lawyer and former Associated Press business and financial reporter who presently is on the staff of the parent law journal.

Both papers will be tabloids and both describe themselves as taking a Wall Street Journal approach to the reporting of legal news and will feature specialty columns by experts in different legal fields. Both want the papers to be tightly edited to make sure busy lawyers not only subscribe to them, but read them. And both will expect large circulation from Washington lawyers.

They differ as to whether there is enough of a community of interest among attorneys in different parts of the country to want to reat a national legal newspaper.

Glasser voted against the national market. "We hope to tap the community of interest in the Washington bar and grow with it," he said.

While the New York Law Journal Fitzhugh agrees that "Washington is a town where you turn around twice and see a lawyer," he added, "the market also exists elsewhere."

"The profession has reached the stage where lawyers want information on how other lawyers practice, not just in their own locality but nationally."

Most legal observers here believe there is room for one weekly law newspaper, but doubt that both can succeed.

Yet both publishing houses are betting big money they can make it. The New York Journal, run by New York political power and millionaire Jerry Finkelstein, has budgeted a $500,000 a year editorial budget and expects to spend about $1 million a year on its publication, to be called the National Law Journal. The planners think they can make money if they hit a circulation of 20,000.

The Harcourt Brace Jovanovich publication, tentatively called the Federal Law Journal, is looking toward a more modest circulation of 10,000. If it succeeds in Washington, there is no question in Glasser's mind that lawyers across the country - wanting to keep track of what's going on among lawyers in Washington - will subscribe.

"The legal business has grown so large," he said, that Washington is no longer a place where the old boy network can keep you in touch."

There is no question the Washington's law business is booming. Anthony Nigro, secretary to the Committee on Admissions for the D.C. Court of Appeals, which regulates the right to practice law in Washington, said an increasing number of out-of-state lawyers are applying for admission to the bar here.

While there are no accurate statistics on the growth of law firms in Washington, Glasser said he has heard of at least 50 out-of-town firms planning to open branches here.

"Washington is an open city for law," he said. "Clients feel they need someone in Washington looking out for their interests."