In 1984, they were in separate camps, divided by one of the sharpest philosophical differences to emerge in a U.S. presidential contest since the Great Depression.

On one side, Robert Beckel and Timothy Finchem were, respectively, manager and finance director of the campaign of Walter F. Mondale. On the other, James Lake and Roger Stone were, respectively, chief spokesman and Northeastern coordinator for Ronald Reagan.

Today, however, the four have joined forces in the kind of political marriage that is solemnized when huge sums of money are riding on the votes of key members of a House committee.

They are conducting a $700,000 lobbying venture to defeat a key element of tax overhaul legislation now before Congress, a provision that would end deductibility of interest paid on bonds issued by states and municipalities to finance hospital, pollution control and other quasigovernment construction. This change would produce $5 billion to $16 billion for the U.S. Treasury over the next five years.

Beckel and Finchem are operating out of their new firm, National Strategies; Lake is with the lobbying firm of Heron, Burchette, Ruckert and Rothwell, and Stone is a partner in Black, Manafort and Stone. And they have set up what amounts to a bipartisan political organization.

Using connections with mayors, governors, businessmen, labor and community officials, their goal is to apply pressure on 17 wavering members of the House Ways and Means Committee. "Between Stone and me, there is really not an area in the country we don't cover," Beckel said.

"It's patterned after a political operation for a campaign," Beckel said. "The concept going in is that you have targeted districts where you have potential votes if there's enough grass-roots support.

"Then you put organizers on the ground, you put a field organizer who's got responsibility for dealing with them every day, and you've got a campaign manager who worries about the funding and accounting."

The tab, which may run as high as $1.2 million, is being picked up by the Public Securities Association (PSA), an organization of investment banks that owes its existence to the tax deductibility of interest on government bonds.

The drive, however, is just one of a host of jobs that Beckel and Finchem have taken on in their new firm. Its office is three blocks down Pennsylvania Avenue from the White House, where both of them might now be working had Mondale won 270, instead of 13, electoral votes.

With David K. Aylward, former chief counsel for the subcommittee on telecommunications, consumer protection and finance chaired by Rep. Timothy E. Wirth (D-Colo.), Beckel and Finchem have become quintessential entrepreneurs of the political marketplace.

They are now involved in corporate takeover fights, in real estate deals from Maryland to Texas, in the marketing of mortgage insurance and golf club memberships, the creation of new trade associations, airport development and in legislative contests between independent television stations and the networks.

In a confidential bid proposal to the homebuilding industry to lobby against restrictions on the importation of timber, the firm proclaimed, "Our organizing network is designed to identify and motivate on behalf of our clients the key state and local opinion-makers, influential political, business and community figures, campaign contributors . . . This type of program adds real clout to state-of-the art, personalized constituent mail campaigns."

The firm told prospective clients that a four-month campaign would cost just over $350,000, including $60,000 for "grass-roots campaign management;" $72,000 for "district-based organizational expenses" in 18 districts at $4,000 per district, and $103,000 for "targeted mail contact" with "professional telephone followup."

Beckel, a liberal Democrat who worked for the Carter administration, numerous Democratic House and Senate candidates and the National Committee for an Effective Congress, pugnaciously defends his activities.

"If I go back through the Peace Corps and the time I've spent electing progressive people to office and the time I spent trying to keep Democratic presidents in the White House, or to elect them -- all that time, I never made a dime . . . ."

"If I can live with myself, then it's perfectly all right. There are an awful lot of progressive Democrats in this town who have made an awful lot of money while I've been working in the vineyards, and I've never been one to criticize them."

National Strategies is taking on one of the most complex collections of clients in Washington, reflecting the different backgrounds of Beckel, Finchem and Aylward.

Beckel says he has participated in 160 campaigns and maintains what amounts to the skeleton of a national campaign staff around the country.

These contacts, he says, are available, for hire, to run local or federal "grass-roots" lobbying drives.

In addition to the PSA, clients include a toxic waste disposal company, Rollins Environmental Services, and, according to other sources, a group of insurance companies who want to limit their liabilities in toxic waste "Superfund" legislation before Congress.

Corporations, trade associations and other groups using grass-roots lobbying are following a fundamental strategy that one of the best ways to persuade an elected official to take any action is to create, if not the genuine article, then at least the impression of a groundswell of local, popular opinion behind the hoped-for action.

In behalf of Rollins Environmental Services, for example, National Strategies set up paid phone bank operations in Brownsville, Tex., to build opposition to the plans of a competitor, Waste Management Inc., to burn toxic wastes at sea.

The callers identified themselves not as employes of Rollins but as representatives of "The Alliance to Save the Ocean."

Finchem, who in the 1984 campaign gained a reputation as an effective fund-raiser, is using his connections with major Democratic donors across the country to market mortgage insurance to savings and loans and other lending institutions, to sell corporate golf club memberships and to set up real-estate development deals.

"Over the years we have developed numerous friends," Finchem said.

"Through the people we know and have met over the years, instead of a marketing firm spending months trying to see the chief executive officer, we can get them in the door."

Finchem recently arranged a trip to Houston's Hobby Airport for 100 Chicago politicians, businessmen, airport board members and other key figures in an effort to build support for a proposal by Southwest Airlines to expand heavily into Chicago's Midway Airport, as it did 10 years ago into Hobby.

Because of his ties to rich contributors, "people are coming to us" looking for ways either to invest money or to obtain capital, Finchem said.

National Strategies now has an equity interest in a 1,500-acre development in Austin, Tex., he said, and is "about to close a deal" on a Montgomery County, Md., upscale residential development where homes will sell for more than $400,000, according to Finchem.

Aylward, the subcommittee staff member, has sought clients whose interests coincide with positions he and Wirth took on Capitol Hill.

"I am known for substantive positions. For me to start representing positions contrary to where I stood for the past five years would shoot one of our strongest selling points," he said.

Among the clients Aylward has picked up are the Independent Television Association, made up of stations not affiliated with a major network, and many of the long-distance telephone competitors to AT&T and MCI.

In an aggressive move that would, in effect, create a client, Aylward is setting out to form a new trade association, the Alliance for Capital Access.

It is made up of corporations specializing in raising capital through high-yield bonds, known in the trade as junk bonds.

This high-risk technique of raising money is threatened by legislators seeking to end use of junk bonds to finance corporate takeovers.

"What we did is, we figured out what we wanted to do, and we figured out how to get someone to pay us for what we want to do," Aylward said.

Beckel said Aylward had worked on legislation changing competition among long-distance companies, adding that "we've got most of the long-distance" competitors as clients.

The idea of setting up a grass-roots organizing operation developed after the 1984 campaign, Beckel said, when he and Finchem realized that their experiences in politics was a substantial resource.

"People who did precincts for us, people who did volunteer work for us . . . people who were paid organizers, people who were mayors, Democratic Party people" -- these political activists, Beckel said, provided an opportunity to set up a different kind of grass-roots service, compared with most Washington-based operations, which use direct-mail techniques to provoke constituents to write their senators or representatives.

Beckel described the rationale. "We thought we have a different slant which is that we would actually take people out and put them on the ground in a congressional district and say,'These are professional organizers and here's what the issue is,' and begin to organize, so that you get quality grass-roots activity . . . .

"You find out it's like organizing for a candidate who's got a particular point of view, who's got a particular constituency. Tax exempt bonds have [as sources of constituent support] school loans, dormitories, waste-water treatment centers, stadiums, you can go down the line and you start to look at all the people who are affected by it, and it sort of becomes an organizer's dream."

Asked about the tactic of creating phony names, such as the Alliance to Save the Ocean, Beckel said criticism of the maneuver is "a lot of bull."

"I've been putting together alliances since the day I got out of the Peace Corps," he added.

"I don't care if it was the Committee to Impeach the President, which I started against Richard Nixon in 1973 and sold bumper stickers, or whether it was the Committee to Save the (C&0) Canal . . . .

"Why does Walter Mondale call his committee the Committee for the Future of America as opposed to the Walter Mondale Committee; why does [Rep.] Jack Kemp call his the Committee for America's Brighter Future? [Kemp's group is called the Campaign for Prosperity.]

"It's so . . . hypocritical to be attacking that, because that's what we do all the time. So we put together alliances of people and we come up with a name of an association or group and we do a campaign. We've done it for years. That's the answer. We got a hell of a good response."

None of the partners in National Strategies would detail how well the firm is doing, although each said it is, in its first year, producing much more money than he had anticipated.

Asked to compare their success with that of a major Republican firm, Black, Manafort and Stone, where partners this year say they may each make $400,000 or more, Finchem said current projections suggest that he, Beckel and Aylward will reach that level within a couple of years.

"This is Year Five for them [Black, Manafort and Stone]. I wouldn't be surprised if we weren't somewhere in their range by the end of Year Three."