A Metro committee yesterday approved a plan to install wheelchair lifts on 50 to 60 more Metrobuses in the next two fiscal years and to create a telephone "reservation" service that would let handicapped passengers arrange for lift-equipped Metrobuses at their stops.

Citizens groups representing the disabled, having lost a fight to get lifts installed in 600 more buses, expressed support for Metro's plan, which will cost about $1 million. It will go before the Metro board next week, where it appears headed for approval.

The plan grew from the Reagan administration's decision last year to ease federal rules that would have required lifts in half the buses in the rush-hour fleets of federally aided transit systems by 1989. The administration also granted wider flexibility in accommodating physically impaired riders.

The new lifts, which could be the last that Metro ever buys, would raise the lift-equipped fleet to about 200 buses, about 15 percent of the peak-hour fleet. Metro already has canceled plans for lifts on 30 new articulated buses that it has ordered.

Officials at Metro and other transit systems have argued that widespread use of lifts is an expensive, wasteful means of making buses accessible. The devices cost about$15,000 apiece, consume more funds in training operators and mechanics and are prone to breakdown, officials say.

Metro currently has about 150 lift-equipped buses. Metro officials point out that the lifts are used for only about 40 one-way rides in any given week.

Groups representing the disabled argue that, despite the problems, lifts play an important role in opening up public transit. Last fall, the Washington Metropolitan Accessible Transportation Alliance, an umbrella organization, called on Metro to put lifts in each of 600 old General Motors buses that are to be rebuilt by the mid-1980s.

Instead, Metro staff members decided to use $900,000 reserved for lifts in 1978 to outfit 50 to 60 Grumman Flxible buses, which unlike the GM vehicles, were designed to have lifts added to them. Under the plan, 20 buses would be done in the year beginning July 1, with another 30 to 40 being equipped the following year, if there are sufficient funds remaining.

Metro also would begin organizing a special reservation program, which officials say would require only a single extra employe. Physically disabled people who phoned a Metro dispatcher at least 24 hours in advance could arrange for a lift-equipped bus to be on a certain route at a certain time. They would be able to arrange one-time service or to have a lift-equipped bus on a particular route regularly.

Metro officials, calling the reservation idea "experimental," say no other city has tried such a scheme. They concede that serious problems remain to be worked out to assure the buses could be shifted from route to route efficiently and without disruption of regular service.

Richard Heddinger, spokesman for the accessible transportation alliance, said the on-call plan has "tremendous potential."

The plan also calls for changes in the use of the 150 lift-equipped buses now in service. Metro officials intend to concentrate them on a smaller number of routes, which handicapped passengers are believed to ride most often.