The Metro board, hoping to arrest the Metrobus fleet's soaring breakdown rate, voted yesterday to seek federal funds for 70 to 80 new buses and to spend $1 million from its own budget on emergency tune-ups for 600 of its most heavily used vehicles.

"We have a fleet that is about at the last stages of its illness," board chairman Jerry Moore said. " . . . There is a direct relationship between the level of maintenance and ridership." Bus ridership has lagged seriously behind the transit system's growth targets in recent months.

Earlier this year, the board decided to concentrate funds on rebuilding old buses, rather than buying new ones. But this week the Urban Mass Transportation Administration created a special, $87 million fund for bus purchases and Metro decided to apply for $10 million of it.

The UMTA program is intended to boost the troubled U.S. bus manufacturing industry. Money for it came from contingency funds in the fiscal 1982 budget and cancelled grants.

If federal officials approve the application, new buses could be on the streets sometime next year. Metro hopes that by spelling the more battered vehicles in use -- 14 percent of the 1,800 buses in the operational fleet were listed as "crippled" in June -- they will improve general service reliability.

Like many other. transit agencies, Metro has grown disillusioned with the new generation of buses produced in this country. Its version of the "advanced design bus," the sleek, tint-windowed General Motors RTS-2, has been prone to breakdown and costly to maintain, officials say.

Metro appears likely to write bid specifications to get so-called "New Look" buses, a general, no-frills design made popular in the 1960s. With the exception of the RTs-2s, Metro's fleet is composed entirely of "New Looks" produced by three different manufacturers.

Among the possible bidders are Grumman Flxible, which is marketing a new bus called the "Metro"; Neoplan, a Colorado-based company which has sold buses to Atlanta and transit agencies in Pennsylvania; and Gillig Corp. of California.

Metro is particularly interested in buses made by General Motors of Canada. They are very similar to the most reliable in Metro's current fleet, New Look models produced in this country in the 1960s by General Motors. However, federal officials say that "Buy America" provisions in federal grants mean the Canadian company could beat U.S. bidders only if its price was at least 10 percent lower.

Under federal rules, Metro cannot select a particular company. Instead, with certain exceptions, it must award the contract to the lowest qualified bidder. Metro officials concede the grant could be a mixed blessing if the contract goes to an unproven model that develops mechanical or operational problems.

Transit officials remember well the cracks that appeared in the frames of Grumman Flxible's brand new advanced design buses in New York and other cities two years ago. The buses were returned to the factory for costly and time-consuming modifications.

Yesterday, the board also voted to use $1 million Metro has saved from lower-than-expected operating costs this year to give extra care to 600 Flxible New Look buses that have become the fleet's workhorses.

Officials say the plan would keep them roadworthy to mid-1983, when Metro expects to have back the first of 600 old General Motors buses that are to be stripped and rebuilt at a cost of $60,000 apiece. That rebuilding program is crucial to Metro's hopes to improve bus service.

In other business, the board:

Sent to U.S. Transportation Secretary Drew Lewis a resolution declaring that area governments have created "stable and reliable" sources of money for operating subsidies. Lewis must certify these steps are adequate before Metro can receive any of $1.7 billion in federal capital funds provided for in 1980 legislation.

Received an award from the American Public Transit Association for improving safety on the Metrobus system. According to Metro, accidents have dropped from 90 per million miles in 1974 to 52 in 1981.