You'd have thought they were selling $2 television sets, the way customers crowded into some Washington area savings and loan associations yesterday to cash in on the last day of high-interest money market certificates.

A teller at Standard Federal recounted how one lady came in bearing a stack of Series E bonds two inches thick which she cashed in for a $10,000 certificate and $7,000 in change. The institution sold $250,000 worth of certificates yesterday compared with only $20,000 worth the previous day.

At Dominion Federal, Vice President George Cain reported a 70 percent increase in sales over the past two days. Washington Federal and Northern Virginia Savings and Loan planned to stay open until 6 p.m. to accommodate savers. In late afternoon, with customers still waiting in line, Washington Federal's assistant vice president Thomas Meehan tallied 67 new accounts, totalling $1 million, of which $800,000 was new money. This compared with $500,000 in sales the previous day.

"Money market certificates, that's all we've done today since we opened up," said Jefferson Federal's vice president for savings operations, Henry Johnson. He said 29 of 33 savings certificates sold were in $10,000 denominations. On Tuesday, half of the money taken in came out of pass-book accounts bearing lower interest rates. But yesterday, all of it represented new funds as customers presented checks from banks and brokers, Johnson continued.

Yesterday was positively the last day for maximum rates at savings and loans. Bank regulatory agencies decreed last week that as of today institutions no longer could compound interest on the certificates, which are pegged to the six-monthly Treasury bill discount rate. And savings and loans no longer may offer a 0.25 percent differential on rates of 9 percent or more.

Credit unions, however, have extended the deadline for maximum rates to March 30. By law, a 10-day notice is required to change rates, and the credit unions could not meet today's deadline.