A new law that expands protection for District of Columbia tenants against their apartments being converted into condominiums has gone into effect without the signature of Mayor Walter E. Washington.

In a message delivered yesterday to the City Council, Washington said he favored the broad intent of the measure, but criticized it as being drafted and passed too hastily by the City Council.

The measure was enacted Nov. 22 as an emergency measure, which means it goes into effect immediately. No hearings were held before its passage.

An existing two-year-old law restricting conversion to condominiums exempts so-called "high rent" buildings, which can be changed without restriction. The new emergency law raises the definition of high rent, putting an uncertain number of additional units under the conversion ban.

The measure increased the legal description of high rent from $162.50 to $205 a month for efficiency apartment, from $212.50 to $247 for a one-bedroom apartment, from $267 to $288 for a two-bedroom apartment and from $375 to 403 for larger units.

In letting the measure become law without his signature, the mayor sidestepped a request that he veto it, made by the D.C. Board of Realtors.

William S. Harps, president of the realty group, sent a letter expressing what he called "vehement objection" to the legislation, contending there was "no evidence . . . that an emergency exists." It is "disruptive, unfair and erratic" to change the rules without notice. Harps wrote.

City Council member Polly Shackleton (D-three), chief sponsor of the emergency measure, denied the Harps assertions and the mayor's criticism that the bill was not fully considered.

Shackleton said the new measure enacts, on a stopgag 90-day basis, approximately the same definitions of high rent as are included in the bill recently passed by the Council extending rent control for three years.

The mayor vetoed a previous version of the rent control measure. He has until Thursday to decide what to do with the newly approved measure.

Without the increased ceilings, Shackleton said, inflation has created a situation where many more units may become vulnerable to conversion. At the time the bill passed, she estimated the higher rent figures might restrict the conversion of six or seven buildings in her yard west of Rock Creek Park and an uncertain number elsewhere in the city.

In his message to the Council, the mayor said the city's Department of Housing and Community Development certified the conversion of 19 buildings containing 842 units during the first six months of 1977. In the next 5 1/4 months - up to the second week of December - a total of 14 buildings were certified that contain 1,042 units.

"This pattern would not appear to suggest that there has been a "sharp increase in conversions" as suggested by the Council, the mayor wrote.