A District rent control official and representatives of city landlords found themselves in rare agreement yesterday. Both were encouraging apartment owners to apply for maximum rent increases allowed under D.C. rent control law.

John T. O'Neill, executive director of the Apartment and Office Building Association, urged an audience of about 100 building owners attending a seminar not to apply "for the quick and dirty automatic increase" that allows landlords to raise rents 10 percent this year but seek a so-called hardship increase that is usually at least double that amount.

He was followed at the seminar on "How to Get a Rent Increase in D.C." by John Hampton, special assistant to the city's rent control administrator, who encouraged landlords to take advantage of all the increases outlined in the city's newest rent control law.

Hampton said later he supports the larger increases, if landlords can justify them, because with additional funds, landlords should be able to maintain their buildings in better condition and thereby benefit their tenants. He acknowledged, however, that some tenants might not be able to afford the steeper rents and could be forced to move out.

The rent control law allows landlords to apply for seven different kinds of increases. The two most common are the automatic increase, which allows landlords to raise rents by 10 percent without city approval, and the "hardship" increase that is allowed if a landlord can prove he is making less than a 10 percent return on his investment as defined by the city.

Landlords can apply for one or the other but not both. Many landlords, especially those with fewer than 100 rental units, often forgo hardship increases because they require documentary evidence that all claimed expenses have been paid and tenants are allowed to challenge the claims.

But landlords who successfully applied for hardships received increases averaging 49 percent during the fiscal year that ended Sept. 30, 1980, the latest year for which figures are available, according to Hampton.

The largest increases occurred in the city's most affluent neighborhoods west of Rock Creek Park where landlords received an average rent increase of 75 percent with hardship petitions, Hampton said. That meant the average monthly rent rose from $239 a month to $428. In the city's poorer neighborhoods east of the Anacostia River, hardship rents rose an average of only 25 percent or from $179 to $212, Hampton said.

Roger Turpin, executive director of Washington Inner Center Self Help, a community group that works with low income tenants, said he opposed the hardship petitions because "in many cases they leave tenants with no choice but to be displaced because they can't afford the higher rent. Their incomes are not high enough to pay for the hardship increases."

But Jim Tamialis, staff director of the Southern Columbia Heights Tenants Union, said he supported hardship petitions "if they are needed to run the building responsibly." He added, "Some tenants have agreed to substantial rent increases of 30 to 35 percent if they can be assured that they will be receiving decent housing that is worth the price."