A significant decline in the nation's money supply in the week ended Feb. 27, reported yesterday by the Federal Reserve, could have a calming effect on financial markets which are anxiously awaiting the Carter administration's economic policy proposals due next week.

The measure of money known as M1-B feel $2.9 billion, to $391.4 billion. M1-B includes coin and currency in circulation as well as all checking deposits at commerical banks and thrift institutions.

M1-A, a narrower measure that does not include checking deposits at thrifts, dropped $2.8 billion, to $374.7 billion, the Fed said.

During the most recent 13-week period, M1-B has been rising at a 7.7 percent annual rate. The latest week's drop, unless quickly reversed which analysts thought not likely, would shortly put growth of the money stock just about in the middle of the Fed's target range.

Markets were rife with rumors credit controls were about to be imposed and that the administration was about to seek authority for wage and price controls. Credit controls were not imposed, and top administration officials again flatly denied they are considering wage and price controls. Late in the week, another rumor -- that a major American bank was about to go bankrupt -- surfaced in several places. Federal banking regulators yesterday emphatically denied any major bank was in serious difficulty.