Officials of Federal National Mortgage Association said yesterday the Washington corporation is doing everything it can to increase mortgage lending for the nation's inner cities.

With federal support, FNMA support for the mortgage markets helped build the suburbs but there "will be a long road back to the city . . . we are trying to erducate the bankers" to invest there, said senior vice president james E. Murray.

Testifying before the Senate Banking Committee, Murray also denounced legislation sponsored by chairman William Proxmire (D-Wis.) and Sen. Alan Cranston (D-Calif.) as a threat to the survival of the "concept" of the company nicknamed "Fannie Mae," a former federal agency charged with the job of channeling money to the mortgage markets.

The legislation, which Fannie Mae officials said is unconstitutional, would increase the size of the company's board of directors by adding fopur new public representatives, named by the President. That would create a shareholder-elected majority of 10-9 compared with 10-5 today.

In particular, Murray cited a 1968 letter from Raymond H. Lapin, then head of the FNMA as an agency and recently named by President Carter to the company's board.

Lapin said, in his 1968 letter, that failure to give stockholders "the controls and management" of FNMA would represent a reneging by Congress of "its solemn promise to stockholders," and would be a violation of the Fifth Amendment.

FNMA and the Washington law firm of Williams and Connolly, hired by teh company to defned its current status, argued that stockholders' rights would be violated by a reduction in their proportional board representation.

Proxmire, however, said yesterday that Attorney General Griffin B. Bell "has assured the administration the bill is legal and constitutional," which the committee chairman said "reflects the depth of administration support" for the measure.

The Wisconsin Democrat also accused FNMA officers with "inciting fears" on the part of stockholders and mortgage lenders and demanded an accounting by the company of all expenses associated with lobbying on legal aid related to the legislation.

He said previous testimony had convinced him that Fannie Maw was "overly restrictive" in its lending standards and was only helping affluent, white people to buy and renovate inner city housing without aiding predominantly black families already living in such homes.

While the company has done a "goog job" in some respects, its failures are "substantial" and could be corrected by the addition of new public members, Proxmire argued.

Citing instances where FMNA officials had declined to make certain information public to citizens and the news media, Proxmire also demanded an accounting of the company's public relations spending. One portion of the Proxmire-Cranston bill would force FNMA to disclose information under the Freedom of Information Act.

Murray said he would provide figures on the spending for defense of the company's case and for public relations, and a spokesman for the firm said yesterday that the 1977 budget for public relations is $621,000. Many large firms spend more than $1 million a year on public relations. Potomac Electric Power Co.'s budget this year, for example, is $1.1 million) Pepco has assets of $1.8 billion compared with $32 billion for FNMA.

In his testimony, Murray also detailed his company's programs designed to increase inner-city lending and provided some new figures on mortgage aid.

In Fannie Mae's program for purchasing conventional mortgages (those not insured by the Federal Housing Administration of Veterans Administration) 26 per cent of the loans have been in urban areas as distinguished from suburban and rural locations, Murray said.

In addition, for 60 per cent of the cases, combined family incomes was $20,000 or less; about half the mortgages covered home purchases by first-time home owners; fourt of five of the mortgages were for resale of an existing home; and one of three homes was built before 1960.

He also described an "aggressive outreach program" to discuss urban lending programs with citizen groups and two minority leaders current or former officers of the United Mortgage Bankers and the National Association of Real Estate Brokers - spoke out yesterday in defense of FNMA practices.