The govenors of Maryland and Virginia and the mayor of the District of Columbia agreed yesterday to impose a regional odd-even gasoline purchase plan beginning Thursday if the long lines of gas-hungry motorists in the Washington area are not significantly reduced before then.

Spokesmen for the three jurisdictions said the plan is a virtual certainty. "Expectations are not very high that situation will improve," a spokesmen for Virginia Gov. John N. Dalton said.

The agreement, announced on Capitol Hill during a meeting of the three chief executives with members of the Washington area congressional delegation, marks the latest effort by state and local authorities to cope with the growing fuel crunch here.

If implemented, it will be the first time the area has had an odd-even sales system since a brief period in early 1974, during the Arab oil embargo. Earlier this spring, 15 densely populated counties in California adopted an odd-even. New Jersey and parts of New York state also will be implementing odd-even this week.

As the chief executive met to plan how to deal with the crisis, motorists throughout the area waited yesterday in lines that appeared to be as long as they were last week.

Service station owners reported that the $5 and $7 minimum purchase requirements imposed in Maryland, the District and Northern Virginia to deter hoarding and "topping off" were almost meaningless, since most motorists were buying far more than the minimum amounts.

Staggering of service station hours - another measure designed to spread the waiting period more evenly throughout the day - has not been implemented on a wide-scale basis and probably will not be for a week or more, officials said.

The more drastic odd-even sales measure announced by Dalton, Maryland Gov. Harry Hughes and District of Columbia Mayor Marion Barry would work this way:

Drivers with license plates ending with an odd digit would be permitted to buy gasoline on odd-numbered days of the month.

Driver with license plates ending with an even digit would be permitted to buy gasoline only on even-numbered days. Zero is considered an even number.

Cars with personalized tags or other tags having only letters would purchase gasoline on even-numbered days.

Saturdays, Sundays, holidays and the 31st of the month would all be considered "open" days, when everyone could purchase fuel. Out-of-state cars not bearing Maryland, Virginia or D. C. tags would be permitted to buy gasoline on all days.

Generally exempt from the plan would be emergency vehicles, hearses, funeral Limousines, cars driven by doctors and nurses, taxis, school buses, commercial trucks and buses, motorcycles and mopeds, construction and agricultural vehicles, van pool vehicles operated by persons who must drive more than 75 miles a day or 400 miles a week, exclusive of commuting.

Processing exemption requests will be a "nightmare," one high-level Virginia official said.

In addition to the odd-even plan, the Metropolitan Washington Council of Governments recommened six measures for local and state authorities to further ease the fuel crunch.

These included a flag system to inform motorists what service stations are open and what type of gasoline they are selling. Under this arrangement, a green flag would indicate leaded gasoline is available and a red flag no gasoline at all.

Other recommendations by the Council of Governments included staggered hours, a review of state gasoline "setaside" programs and requests for increased allocations from the oil companies.

Current minimum sales requirement -$5 for cars in Northern Virginia and the District, and $5 for small cars and $7 for large cars in Maryland - would remain in effect.

If Hughes, Dalton and Barry decide the gasoline lines have not been substantially shortened by tomorrow, the odd-even plan will go into effect at 12:01 a.m. Thursday.

The plan would apply to the District of Columbia, the nine principal suburban Virginia jurisdictions and portions of Maryland. Maryland officials said Hughes had no decided late yesterday whether to apply the odd-even plan statewide or restrict it to the Washington and Baltimore metropolitan areas, where the crunch has been the most serious.

The nine Virginia jurisdictions are Fairfax, Arlington, Loudoun and Prince William counties and the cities of Alexandria, Fairfax, Falls Church, Manassas and Manassas Park.

During the Arab oil embargo in 1974, a mandatory odd-even plan was imposed briefly in Virginia and Maryland. In the District of Columbia, the plan was voluntary. The plans appeared to reduce gas lines in most areas.

Dalton, Hughes, Barry and several members of Congress yesterday questioned what they said appear to be disproportionately large reductions of fuel allocations by the major oil companies to the Washington area.

Rep. Clarence D. Long (D-Md.) asked if the shortage was contrived by the oil companies to "influence members of Congress" to support price deregulation of the industry.

Rep. Barbara Mikulski (D-Md.) asked if Hughes, Dalton or Barry had considered suing the oil companies "to get them to fulfill their social contract." Hughes said he is awaiting an opinion from the Maryland attorney general on that question.

The three chief executives repeatedly said their jurisdictions are receiving 15 to 25 percent less fuel than this time last year, and that these reductions appear greater than those suffered by most other regions of the counry.

Rep. Herbert E. Harris II (D-Va.), who organized the congressional delegation meeting, also sharply question federal Energy Department officials who came to the meeting. Harris suggested that they had not used their regulatory powers to compel the oil comapnies to divert larger allocations to the Washington area.

Harris said he hoped to call Energy Secretary James R. Schlesinger and other top DOE officials to a hearing, possibly later this week, to answer these and other questions.

Mammoth gasoline lines continued to be the rule throughout much of the Washington area.

"The line is longer than it was before," said Coy Miles, manager of the Bladensburg Amoco at 814 Bladensburg Rd. NE. "I don't think it [the minimum purchase requirement] has had any effect at all."

Motorists are "buying like normal," he said, pointing to a line of cars coiled around three blocks nears his station.

Last evening, motorists bunched together at at least two stations in mile-long lines to take advantage of a special shipment of gasoline that the District allocated to eight stations open from 7 p.m. to 9 p.m.

At one of them, the Pennsylvania Avenue Amoco Station at 2500 Pennsylvania Ave. SE, irate motorists waved their fists and shouted "Get them, get them," to city police Sgt. Lloyd Coward, who told three drivers to move from the line after they had forced their way in.

Coward said the line formed long before 7 p.m. By 7:45 p.m., ploice placed a "last car" sign on a bronze length of the line that snaked around the blocks almost twice. CAPTION: Picture, On the Hill: Rep. Herbert E. Harris II, left, Virginia Gov. Dalton, Maryland Gov. Hughes, D.C. Mayor Barry.By James M. Thresher - The Washington Post