Council of Economic Advisers Chairman Murray Weidenbaum, a key member of the top Reagan economic team, keeps a low profile, but his colleagues say he has increasing influence on both domestic and international economic policy.

"Murray is a guy who emerges over time as someone you lean on for good quantitative work and common sense," says Deputy Treasury Secretary Tim McNamar. "He's the glue that holds the rest of the economic advisers together." Initially, some observers of the Washington scene thought that Weidenbaum would focus on his special interest -- government regulation -- and on other microeconomic topics.

But as chairman of the council, Weidenbaum has been into everything. He produced the basic macroeconomic paper for the U.S. team at the Ottawa summit, for example, and has played a leading role in the explication of American economic policy to U.S. partners in Europe.

In a wide-ranging interview, Weidenbaum made clear that the dominant approach of the Reagan administration on all economic issues is to rely on the free market, but not blindly. In response to my questions, this is how Weidenbaum sees current problems: BUDGET DEFICITS

Q: Will there be a conflict within the administration next year between the objectives of a balanced budget and rising defense expenditures?

A: We all believe in two things. One, we need a stronger defense. Two, we need a balanced budget in fiscal year 1984.We need a proper weighting, not a choice between those two objectives.

Q: If a balanced budget is not in views as 1984 approaches, would the president go to a value-added tax or other tax so as to balance the budget?

A: This administration didn't come here to raise taxes. Now, user fees, where apprpriate, might be raised. But new taxes? They are not on our agenda. TAX POLICY

Q: Didn't you get a lot more than you bargained for in the big tax bill passed by Congress?

A: If you look at it, 80 percent of what passed was the original 'clean bill' -- that is, Kemp-Roth and accelerated depreciation. Another 10 percent or so was for two major additions, indexing and the marriage penalty. So all the other 'ornaments' come to less than 10 percent. On balance, it's a good bill. INTEREST RATES

Q: Why aren't interest rates coming down as inflation recedes?

A: Interest rates will come down later this year when we see better news in inflation. The era of double-digit interest rates is behind us. TAKEOVERS

Q: Are you concerned by the rash of recent takeovers and merger attempts?

A: No, private enterprise is private enterprise. I would be concerned only if some of these efforts represented government bids to take over.

Q: How about the Seagram's effort to take over Conoco?

A: Private enterprise is private enterprise! WAGE POLICY

Q: I can't figure out what your wage policy is, or whether you have one.

A: Yes, we do have a wage policy, although it is true we don't believe the administration should be involved in the process of private wage negotiations. Coal, not the controllers' strike, is the prototype. We believe strongly that the private market will restrain wage and price decisions: When they get to be non-competitive, they will suffer. The government must reduce current inflation so that COLAs [cost of living adjustments] don't push up prices. Also, government must set a climate so that bargaining can take place in the expectation of less inflation. TRADE

Q: How pure is the Reagan policy on free trade?

A: I like to say: 'Don't just stand there, undo something!' We have a responsibility to refrain from actions that interfere with competitive markets. We're against credit subsidies. We're against targeted assistance. In my role as an adviser to the president, I want to set out to the desirable approach, which is a market approach, recognizing that we all operate in real world where exceptions must be made. THIRD WORLD

Q: What position will this government take at the North-South summit in October in Cancun, Mexico?

A: We will take a more positive position than a lot of people expect at the Cancun summit, as indeed we did at Ottawa on North-South problems. But if they [the poor nations] want the most effective form of aid, they should copy from our own formula, that is, benefiting from private capital. Look, in the 19th century, Europe infused capital into America, and that's why we prospered. Economic development is primarily a task for the private sector. Government's role is to set up an environment that is conducive to private investment, not one that scares it away.

Q: There doesn't seem to be much of a role for government, then.

A: There is a role for government. We're not a nihilist society. That role is to take care of infrastructure highways, education and so on. ENERGY

Q: How about the argument that private multinational oil companies won't invest in Third World oil development unless assured there is an export market -- as well as local oil development -- and therefore, you need World Bank financing to get the job done?

A: That answer can be found in Economics 1. If there's not enough oil to export, it would be best for the developing nation involved to invest its resources in something else, and buy the oil they need. They would have some money left over.

Q: Suppose the concern is for the security of these importing nations who have an excessive dependence on OPEC oil?

A: That's not the concern of the World Bank.

Q: The bank in its new World Development Report says that the poor countries' energy development will cost $40 billion a year for the next five years. Can the private sector manage that?

A: I don't know how they got that figure, but sight unseen, I'm very suspicious [of it]. I don't that any one country has a stake in reducing the oil dependence of another. OPEC created the problem, and it's one they should solve. FOREIGN AID

Q: You don't seem to be sympathetic to the Third World plight.

A: I try to be sympathetic. But I want to identify the source of the problem. Economic doctors don't commiserate with the patient -- that's just a bedside manner. The economic doctor should prescribe serious remedies. If Party A does something to Party B, and Party B looks to Party C for a cure, something is out of kilter.

You know, lots of nations have a different life style from what they scorn as the materialism of the West --to adopt. They point to the serious social costs of our materialistic life style. But the idea that they want to share the benefits -- but not the costs -- of our life style leaves me cold.

Of course, you don't have to go abroad -- you can find parallels in our own country, like the dropouts who don't mind showing up for their monthly checks. I take a hard line on domestic claimants on our budget, so my attitude on foreign claimants is not discriminatory.

Q: How about complaints from our European partners that we don't pony up our fair share of development assistance?

A: These complaints lack perspective. Since the end of World War II, we have been a most generous, caring society. Now, some other nations have some catching up to do, and we're happy to have them do it.