The battle of the "D line-the zoning line demarcating areas where diplomatic missions may establish chanceries-raged at the D.C. Zoning Commission this week.

At stake was approximately 62,000 square feet of land, next to the Iranian Embassy and Chancery at Massachusetts Avenue and 30th Street NW, which the embassy wants to rezone. Approval of the rezoning would allow the Iranians to use the top floor of a house at 2500 30th St. NW for embassy offices.

The battle before the Zoning Commission Monday was waged by lawyers in three-piece suits, well-groomed matrons in navy blue, bureaucrats bearing reports, architects wielding complicated charts and, in absentia, the government of Iran.

No embassy members were present. However, George Sealey Jr., of the State Department, urged the commission to grant the zoning change.

Attorney Sylvan Marshall, who presented the Iranian government's case, said "recent cash-flow problems" had prompted the embassy to consider closing offices in various locations and consolidating its operation in the present chancery behind the embassy. To ease crowded conditions at the chancery, the Iranians propose using the top floor of the 1920s mansion for offices for 14 people. The mansion, known as "Interlude," is adjacent to the embassy property but fronts on 30th Street NW, a residential street.

Converting the top floor to offices, said Marshall, could be accompliished if the Zoning Commission would move the D-line south a "grand total of 295 feet." The D-line now runs through the Iranian government property.

"How could 14 people moving into 3,600 feet of office space cause the catastrophe envisioned by the opposition?" asked Marshall.

Marshall said he had been assured by Iranian officials that the building was not being used for embassy business and now is occupied only by a caretaker and his family.

Those opposed to the plan listed several objections.

The neighborhood doesn't want what used to be a house and a home and a neighbor to become a business," said Thomas G. Corcoran Jr., who represented four homeowners in the wealthy Normanstone neighborhood.

Corcoran and others alleged that the house, which was renovated last summer, already was being used for embassy offices.

Advisory Neighborhood Commissioner David Grinnel said the ANC had written a letter Jan. 26 asking the city zoning regulaion office to investigate whether the house was being used illegally as a chancery.Grinnell said the ANC had not received a reply.

Zoning Commission Chairman Ruby B. Mczier told Grinnell she would arrange for a city inspection of the building.

Wayne W. Parrish, who lives on the corner of 30th Street and Benton Place, complained that the embassy already had caused traffic and parking problems in the area.

Marshall countered that those protesting were "a very small group who want to keep a few streets free of traffic." He said the embassy would agree to prohibit its staff from parking on 30th Street, would not allow vehicles access to the property from that street and would require all personnel to enter Interlude from the rear, through the embassy grounds.

Chhairman Mczier pointed out, however, that the commission could not grant a zoning change that is based on any conditions such as those propsed.

Neighbors of the Interlude were not mollified by the embassy promises.

The citizens' protest was backed by the Assistant City Administrator for Planning and Development James O. Gibson.

Gibson said the D-line was drawn to include only the Massachusetts Avenue front-age of the Iranian property and to exclude the portion of the Iranian property that lies in the reiidential area.

The victor in the battle of the D-line is expected to be decided at the Zoning Commission's May 10 meeting.