The Federal Home Loan Mortgage Corp., which began marketing its securities through Wall Street last month, sold $575 million worth in the first 3 1/2 weeks, or as much as the corporation itself sold in a three-month period last year, officials report.

Mortgage Corp. president Victor H. Indiek says he expects sales to level the $1.5 billion record set last year. In January the corporation began a campaign, with the participation of eight leading brokers, to induce more institutional customers such as pension and trust funds an insurance companies to purchase its offerings.

Known as Freddie Mac, the corporation is a government-charactered entity that buys and sell more conventional residential mortagages than any other institution in the country. The two other entities created by Congress to deal in the secondary mortgage market are the Federal National Mortgage Association (Fannie Mae), which buys certain types of FHA and VA mortgages to asist low and middle income homebuyers.

In repurchasing mortgages from savings and loan associations, Freddie Mac shifts excess mortgage money to those areas that need it.

It also serves to hinder disintermediation, or the flow of mortgage funds away from thrift institutions when better rates are available from other markets.

Through Freddie Mac's efforts to standardize underwriting procedures from state to state, about a quarter of all conventional mortgages are now repurchased on the secondary market, up from 13 per cent in 1970 when the entity was established, its official say. In 1976 it bought and sold more than $1.4 billion worth of conventional mortgages out of a total of $500 billion outstanding nationwide.

Indick says the corporation has been profitable since its establishment. To assure a firmer foundation, last year it began to hedge its risks by using the Ginnie mae futures market on the Chicago exchange.

The corporation is conducting seminars for analysts around the country this spring to try to boast sales of securities, called participation certificates (PCs), to $8 billion in 1977, Indiatik said.

PCs are sold each business day in denominations from $100,000 up to $1 million. Interest and principal payments are passed through monthly as received by Freddie Mac, which guarantees then unconditionally.

They are classified as mortgages for tax purposes. The current yield is 7.92 per cent, compared with 7.76 per cent for Ginnie Mae offerings. Last August Mortgage Corp. PCs paid 8.45 per cent.

The Mortgage Corp. also offers Guaranteed Mortgage Certificates (GMCs) which have bond-like characteristics in theat they pay interest and principal annually in specified minimum amounts. Indiek predicts that GMC sales will total $400-$500 million in 1977.