Conrail and the Brotherhood of Railroad and Airline Clerks yesterday reached an agreement in principle on a 39-month contract retroactive to Jan. 1, 1978, officials said.

The new pact will cover 20,000 railroad employes, accrding to BRAC President Fred J. Kroll.

A union spokesman said the new contract negotiated in Philadelphia calls for wage and fringe benefit increases of 36 percent over the 39month period.

The terms are the same as those negotiated in the national agreement reached between the AFL-CLOiaffiliated union and the nation's other railroads Jan. 13, the spokesman said.

That package was ratified by 5 to 1 by railroad employes, the splkesman said. Conrail employes voted for the January agreement despite Conrail's withdrawal from the talks, the spokesman said.

Conrail is the federally chartered rail system created in 1976 to take over the operations of the bankrupt Penn Central and other eastern railroads.

Meanwhile, yesterday's reports of soaring consumer prices reduced further the chances of a Teamsters union contract settlement within President Carter's wage guidelines.

Even industry bargainers, who have been sticking by the 7 percent wage standard, acknowledged it may be an unattainable goal.

The government's announcement yesterday that consumer prices rose at an annual rate of more than 15 percent in February "complicates accptance of the wage and price standard by the union," said J. Curtis Counts, the industry's chief bargainer.

Teamsters President Frank Fitzsimmons said the news "puts me in my (original) position." By this, he apparently menant the union could go along with the guidelines only if they were modified and were showing signs of slowing the pace of inflation. Neither condition has been met, a union aide said.

At the Teamster talks, sources close to the negotiations indicated that contract issues were hardly discussed bycause of preoccupation with the inflation rate and the government's policy for coping with it. As of late yesterday, no talks were scheduled for the weekend. Union locals will be meeting over the weekend to take strike autorization votes. Authorization is expected to be granted.

The two sides remain far apart. The union, angry when the government refused to water down its 7 percent wage guideline, demanded a pay increase of roughly 14 percent for the first year of a three-year contract. The industry countered with an offer of 6 1/2 percent for the first year, and there reportedly have been no further offers.