It is 4:10 p.m. Treasury Secretary Donald T. Regan strolls over to a computer terminal behind his desk and punches a few keys. ''I want to check the markets and see how they closed,'' he says. The first thing the former Wall Street executive punches up on his computer screen is information on the US dollar. Earlier that day the currency had come under strong selling pressure, although it recovered somewhat in late trading.
Mr. Regan is not alone in keeping a close eye on the dollar. In the past five weeks the dollar has dropped 3.5 percent against major foreign currencies. And the dollar's decline against the West German mark has been even sharper - down 5 .5 percent between Jan. 9 and Feb. 15.
Regan is careful not to forecast what the dollar will do in coming days. ''Far be it from me to predict what will happen,'' he says in an interview.
But he adds that a significant decline ''wouldn't surprise us,'' given the bleak 1984 forecasts for the United States trade balance and the broader current account measure.
Other experts are divided on whether the dollar's recent decline may signal the start of a sharp, near-term drop or is the beginning of a more gradual decline. But either course would have a significant impact on consumers' finances.
A variety of factors are eroding the dollar's appeal, currency traders say. These factors include the decline in the US stock market, a perception that other currencies - including the mark - were undervalued, and growing worries about large US budget and trade deficits.
There has been ''a change in sentiment due to (predictions of record) trade deficits,'' says Elaine Clifford, a currency trader at New York's Irving Trust Company.
''We see this being the beginning of a long-term decline of the dollar over the next three years. But of course there will be fluctuations . . . in that period,'' says Jonathan Francis, currency forecasting director at Wharton Econometric Forecasting Associates. He says he thinks that the dollar may recover a bit in the next several days but drop about 5 percent by the end of 1984.
A smaller group of analysts notes that the recently issued Economic Report of the President said the dollar was overvalued by as much as 32 percent, and they say the short-term drop could be pronounced.
''A major crisis is inevitable, although it is impossible for economists to predict the timing,'' says Stephen Marris, senior fellow at the Institute for International Economics. He says the correction in the dollar's value could be rapid and ''a good deal more than 20 percent.''
There is little disagreement that a weakening dollar will cause significant changes in the average citizen's wallet or pocketbook. One effect: Imported goods suddenly become more expensive, because each dollar buys a smaller amount of the foreign currency that merchants need to purchase such goods. These rising prices for imports push up the US inflation rate.
''If the dollar comes down, the price level will rise,'' Martin Feldstein, chairman of the President's Council of Economic Advisers, told reporters earlier this month. He estimates that each 1 percent fall in the dollar adds 0.5 percent to the US inflation rate. A declining dollar also makes investments in US securities less appealing to foreign investors. As a result, the flow of foreign capital into the US could decline, pushing up the nation's interest rates.
Secretary Regan cautions that this process is not automatic. ''What is the demand side of the equation?'' he asks. ''Is business going to really want all'' the money foreign investors now are providing?
However Federal Reserve Board chairman Paul A. Volcker recently told Congress that if the flow of foreign investment tapers off before the federal budget deficit is trimmed, ''housing and investment will be squeezed'' by the resulting higher interest rates.
A falling dollar also has its bright side. A weaker dollar boosts US exports, because foreign purchasers can buy more dollars with each unit of their local currency. So US goods become less expensive in overseas markets.
''If the dollar declines precipitously, we are apt to turn this trade deficit around faster than people think,'' Regan says. Due to recent efforts to boost productivity, US manufacturers ''will be extremely competitive with the rest of the world,'' if the dollar come down, he says.
Without that help, US exports are expected to lag imports by a record $100 billion or more in 1984, forecasters say.
Finally, a declining dollar makes it easier for less-developed nations to pay their debts, which are denominated in dollars.
Like all markets, currency trading often is affected as much by psychological factors as by specific events.
Traders say, however, that some downward pressure on the dollar has resulted from the decline in the stock market. Analysts say that between 3 and 5 percent of the money that came into the US in the last year now has left. When investors take money out of the US, they may sell dollars and buy another currency, thus exerting downward pressure on the dollar.
The dollar's weakening against the West German mark occurred because the mark ''was so oversold'' and because the West German economy is improving, says Mr. Francis of Wharton Econometric Forecasting Associates. ''There is a modest economic recovery that is continuing in West Germany.''