(Adds details on extent of blockades, government response)
SAO PAULO, May 25 (Reuters) - A nationwide truck drivers' protest in Brazil was slow to wind down on Friday despite an agreement to end the mobilization, with many highway blockades in place for a fifth straight day rattling sectors of the economy ranging from agribusiness to auto factories.
Negotiators for several trucker groups agreed late on Thursday to suspend the mobilizations for 15 days after the government vowed to subsidize and stabilize diesel prices, which may cost 5 billion reais ($1.4 billion) this year.
To win over truckers, who began the blockades on Monday to protest high fuel prices, the government also promised to extend for 30 days a 10 percent diesel price cut announced by state-led oil company Petroleo Brasileiro SA.
Shares of Petrobras, as the company is known, rose more than 2 percent in early trading after plunging 19 percent in the prior two days, as news of government subsidies softened the blow of political interference in the firm's fuel pricing.
Abcam, a trucking group that was a major force behind the strike, was not among the parties that signed the accord, raising questions about how truckers around the country would respond to the agreement.
Brazil's federal highway police said there were still blockades present in 24 of the nation's 26 states, with 74 just in the southern state of Rio Grande do Sul, which is a key route for trade with neighboring Argentina.
Major routes between cities such as Sao Paulo, Rio de Janeiro and Belo Horizonte also remained blocked. Private port operator Codesp SA said there was nearly no activity at Santos, the busiest port in Latin America.
Gas stations remained short of fuel and grocers' aisles were understocked in many areas. Public transport and trash collection were reduced in major cities due to fuel shortages.
Fibria SA, the world's largest producer of eucalyptus pulp, said the protests were affecting its production and transportation.
Auto production in Brazil, which contributes about a quarter of industrial output, ground to a halt on Friday, according to carmakers association Anfavea, in the latest blow to a fragile economic recovery following the worst downturn in decades.
The truckers' protest has weakened Brazil's unpopular government, whose market-friendly reform agenda had already stalled ahead of a wide-open October election.
Raul Jungmann, minister of public security, said the government will investigate if trucking companies were prohibiting employees from working, breaking "lockout" laws.
($1 = 3.65 reais) (Reporting by Gram Slattery and Jose Roberto Gomes Editing by Brad Haynes and Dan Grebler)