Ralph Stanley and don Reno--who each turned 55 last week--rank with Earl Scruggs as the pioneers of the five-string bajo in bluegrass music. Last night at the Museum of Natural History the two self-effacing leaders left most of the soloing to their younger sidemen. Stanley's Clinch Mountain Boys and Reno's Tennessee Cut-Ups were admirably proficient but lacked the loose spart that once made bluegrass a vital folk music.

Ralph Stanley described his music as "the olt-time mountain style of what they call bluegrass." His claw-hammer-picking of banjo arpeggios, his band's clean, simple lines and the high nasal vocals reflected this traditional approach. don reno employed a more progressive style: single-not leads that construct and embroider inventive harmonies. His band of flashy soloists -- including two of his sons -- could learn from his directness.

The Department of Commerce will release on Monday the composite indexes of leading, coincident and lagging indicators and construction expenditures for January.

Also on Monday, the Department of Labor will release figures on productivity and costs in the nonfinancial corporate sector for the fourth quarter of 1981.

On Tuesday, the Department of Commerce will issue data on sales and inventories of single-family homes for January.

The Department of Commerce will release on Wednesday figures on manufacturers' shipments, inventories and orders for January.

The Federal Reserve Board will release on Wednesday selected interest rates for February.

The Department of Labor will issue on Friday data on the employment situation for February.

The Federal Reserve Board will release on Friday figures on consumer installment credit for January.