Virginia authorities have approved a $72.5 million loan that should insure transformation of Alexandria's aging Shirley Duke-Regina apartments into the largest low- and moderate-income housing complex in Northern Virginia.

The loan by the Virginia Housing Development Authority, an agency that funds housing projects statewide, apparently ends a two-year delay in renovation of the complex, which Alexandria officials have said is sorely needed in the apartment-starved area.

The loan, financed by the sale of tax-emept mortgage bonds and notes on the open market, is by far the largest in the seven-year history of the state agency, a spokesman said yesterday. The largest previous loan was $6.4 million for a project in Henrico County near Richmond.

Baltimore developer Morton Sarubin, who purchased the 2,113-unit complex in 1978 after its previous owners went bankrupt, said yesterday that full-scale renovation work will begin in March and the first tenants may be able to move in within six months.

"I'm very happy -- this makes everything worthwhile" said Sarubin, who said renovation of the entire project is expected to take 28 months.

Alexandria officials also reacted with optimism to yesterday's announcement.

"There is virtually no new construction of rental units anywhere in the area," said Mayor Charles E. Beatley. "I'm very happy."

The boarded-up, 30-year-old complex, located on a 76-acre site between Duke Street and Shirley Highway in the west end of Alexandria, is expected to provide housing for up to 5,000 people when renovation is completed, city officials said.

Sarubin said rentals will range from $300 a month for a one-bedroom apartment to $500 monthly for a two-bedroom unit. In addition, "boutique-type stores" will be located in the West End Shopping Center, part of the complex that now houses an adult movie theater, several small restaurants and a laundromat, he said.

Nearly half of Alexandria's crimes in the late 1970s could be traced to residents of the decaying complex, according to police fitures. Its closing in the spring of 1978 forced the eviction of more than 4,000 low-income tenants, many of whom relocated in other poor sections of Alexandria, Arlandria and the Rte. 1 corridor in southern Fairfax County.

Demands by city officials that subsidized units be included in any renovation plan for Shirley Duke-Regina have been a key issue in the two-year controversy.

Neighboring tenants and property owners have expressed fears that including subsidized units would encourage more crime. But city officials, citing the conversion of 3,500 rental units to condominiums in the last four years, argued that the city desperately needs more rental units for the elderly and the poor.

Last fall, after several tumultuous meetings with city officials and residents, Sarubin agreed to set aside 423 units -- 20 percent of the complex -- for subsidized apartments.

The City Council then approved his plans, which hinged on getting the loan from the state that was finally approved Tuesday night and announced yesterday.

Under the financing arrangements worked out by Sarubin and the National Corporation for Housing Partnership, a general partner with Sarubin in the venture, the $72.5 million loan will cover most of the currently anticipated renovation costs of $76.24 million.

The U.S. Department of Housing and Urban Development last year agreed to insure the project for the full $76.24 million but the work could not be started until the state issued its $72.5 million loan.

Additional funds for the renovation are expected to come from private investors.