President Biden is expected to propose a $6 trillion budget on Friday that would lay the foundation for his plans to modernize the nation’s infrastructure and expand the government’s role in providing healthcare, education, and other social services, according to people familiar with the plans.The Biden administration’s first budget, for the fiscal year starting Oct. 1, would be the nation on a path to spend $8.2 trillion annually by the end of 2031. Under this plan, debt would surpass the record seen at the end of World War II within a few years and reach 117% of economic output by the end of 2031, up from roughly 100% this year.The government was on track to spend $5.7 trillion in the fiscal year 2021, according to Congressional Budget Office projections released in February, before Congress enacted Mr. Biden’s $1.9 trillion Covid-19 relief package. The Biden budget plan would boost federal spending by $300 billion, or 5%, above the 2021 projected level.The budget request, which usually reflects an administration’s policy priorities, is expected to detail the proposals Mr. Biden has already laid out in his infrastructure and family-aid plans over the past few months. Officials have stated that those plans, which envision sharply higher taxes on corporations and the rich, will generate enough revenue to balance higher spending within 15 years, but will add to deficits in the meantime.